diff --git a/cmd/sorg-build/main.go b/cmd/sorg-build/main.go
index 84e5edb11..e6e4c364d 100644
--- a/cmd/sorg-build/main.go
+++ b/cmd/sorg-build/main.go
@@ -57,9 +57,9 @@ type Article struct {
 	// Hook is a leading sentence or two to succinctly introduce the article.
 	Hook string `yaml:"hook"`
 
-	// HookImage is a boolean indicating whether there's a preview image for
-	// the article that can be shown on the index page.
-	HookImage bool `yaml:"hook_image"`
+	// HookImageURL is the URL for a hook image for the article (to be shown on
+	// the article index) if one was found.
+	HookImageURL string `yaml:"-"`
 
 	// Image is an optional image that may be included with an article.
 	Image string `yaml:"image"`
@@ -81,10 +81,6 @@ type Article struct {
 	// included as YAML frontmatter, but rather calculated from the article's
 	// content, rendered, and then added separately.
 	TOC string `yaml:"-"`
-
-	// TwitterImage is a boolean indicating whether there's an image for
-	// the article that can be shown in a Twitter card.
-	TwitterImage bool `yaml:"twitter_image"`
 }
 
 // PublishingInfo produces a brief spiel about publication which is intended to
@@ -193,10 +189,6 @@ type Fragment struct {
 
 	// Title is the fragment's title.
 	Title string `yaml:"title"`
-
-	// TwitterImage is a boolean indicating whether there's an image for
-	// the article that can be shown in a Twitter card.
-	TwitterImage bool `yaml:"twitter_image"`
 }
 
 // PublishingInfo produces a brief spiel about publication which is intended to
@@ -583,12 +575,26 @@ func compileArticle(dir, name string, draft bool) (*Article, error) {
 		return nil, err
 	}
 
+	format, ok := pathAsImage(
+		path.Join(sorg.ContentDir, "images", article.Slug, "hook"),
+	)
+	if ok {
+		article.HookImageURL = "/assets/" + article.Slug + "/hook." + format
+	}
+
+	if err != nil && !os.IsNotExist(err) {
+		return nil, err
+	}
+
 	card := &twitterCard{
 		Title:       article.Title,
 		Description: article.Hook,
 	}
-	if article.TwitterImage {
-		card.ImageURL = sorg.AbsoluteURL + "/assets/" + article.Slug + "/twitter@2x.jpg"
+	format, ok = pathAsImage(
+		path.Join(sorg.ContentDir, "images", article.Slug, "twitter@2x"),
+	)
+	if ok {
+		card.ImageURL = sorg.AbsoluteURL + "/assets/" + article.Slug + "/twitter@2x." + format
 	}
 
 	locals := getLocals(article.Title, map[string]interface{}{
@@ -710,14 +716,15 @@ func compileFragment(dir, name string, draft bool) (*Fragment, error) {
 	// A lot of fragments still have unwritten hooks, so only add a card where
 	// a fragment has a configured Twitter image for the time being.
 	var card *twitterCard
-	if fragment.TwitterImage {
+	format, ok := pathAsImage(
+		path.Join(sorg.ContentDir, "fragments", fragment.Slug, "twitter@2x"),
+	)
+	if ok {
 		card = &twitterCard{
+			ImageURL:    "/assets/fragments/" + fragment.Slug + "/twitter@2x." + format,
 			Title:       fragment.Title,
 			Description: fragment.Hook,
 		}
-		if fragment.TwitterImage {
-			card.ImageURL = sorg.AbsoluteURL + "/assets/fragments/" + fragment.Slug + "/twitter@2x.jpg"
-		}
 	}
 
 	locals := getLocals(fragment.Title, map[string]interface{}{
@@ -2113,6 +2120,25 @@ create:
 	return os.Symlink(source, dest)
 }
 
+// Checks if the path exists as a common image format (.jpg or .png only). If
+// so, returns the discovered extension (e.g. "jpg") and boolean true.
+// Otherwise returns an empty string and boolean false.
+func pathAsImage(extensionlessPath string) (string, bool) {
+	// extensions must be lowercased
+	formats := []string{"jpg", "png"}
+
+	for _, format := range formats {
+		_, err := os.Stat(extensionlessPath + "." + format)
+		if err != nil {
+			continue
+		}
+
+		return format, true
+	}
+
+	return "", false
+}
+
 func renderView(layout, view, target string, locals map[string]interface{}) error {
 	log.Debugf("Rendering: %v", target)
 
diff --git a/content/articles/acid.md b/content/articles/acid.md
index 06151484c..eacbe5744 100644
--- a/content/articles/acid.md
+++ b/content/articles/acid.md
@@ -6,8 +6,6 @@ hook: On ensuring system integrity, operability, and
   correctness through a solid foundational database, and
   how ACID transactions and strong constraints work in your
   favor. Why to prefer Postgres over MongoDB.
-hook_image: true
-twitter_image: true
 ---
 
 In 1983, Andreas Reuter and Theo Härder coined the acronym
diff --git a/content/articles/api-paradigms.md b/content/articles/api-paradigms.md
index 4b8e7ecb4..7be31f033 100644
--- a/content/articles/api-paradigms.md
+++ b/content/articles/api-paradigms.md
@@ -5,8 +5,6 @@ location: San Francisco
 hook: Musings on the next API technology, and whether REST-ish
   JSON over HTTP is just "good enough" to never be displaced
   in a significant way.
-hook_image: true
-twitter_image: true
 hn_link: https://news.ycombinator.com/item?id=14003134
 ---
 
diff --git a/content/articles/breaktime.md b/content/articles/breaktime.md
index 9603e8ef1..f61c3d97c 100644
--- a/content/articles/breaktime.md
+++ b/content/articles/breaktime.md
@@ -4,7 +4,6 @@ published_at: 2014-02-02T18:15:28Z
 location: San Francisco
 hook: In search of an alternative to BreakTime. The
   discovery of a very classical solution.
-hook_image: true
 ---
 
 A few years ago I took the plunge and started using
diff --git a/content/articles/heroku-values.md b/content/articles/heroku-values.md
index ff595480f..7dc5623b5 100644
--- a/content/articles/heroku-values.md
+++ b/content/articles/heroku-values.md
@@ -4,8 +4,6 @@ image: "/assets/heroku-values/heroku-values.jpg"
 location: San Francisco
 published_at: 2015-11-05T06:20:16Z
 title: My Heroku Values
-hook_image: true
-twitter_image: true
 hn_link: https://news.ycombinator.com/item?id=14286143
 ---
 
diff --git a/content/articles/idempotency-keys.md b/content/articles/idempotency-keys.md
index 8ea9fb73a..63a36e269 100644
--- a/content/articles/idempotency-keys.md
+++ b/content/articles/idempotency-keys.md
@@ -6,8 +6,6 @@ hook: Building resilient services by identifying foreign
   state mutations and grouping local changes into
   restartable atomic phases so that every request can be
   driven to completion.
-hook_image: true
-twitter_image: true
 hn_link: https://news.ycombinator.com/item?id=15569478
 ---
 
diff --git a/content/articles/interfaces.md b/content/articles/interfaces.md
index f1d90a256..9add4cc9d 100644
--- a/content/articles/interfaces.md
+++ b/content/articles/interfaces.md
@@ -5,8 +5,6 @@ location: San Francisco
 hook: How we overvalue the wrong technology and novel
   aspects of interface design at the expense of substantial
   gains to our productivity.
-hook_image: true
-twitter_image: true
 hn_link: https://news.ycombinator.com/item?id=13733777
 ---
 
diff --git a/content/articles/minimalism.md b/content/articles/minimalism.md
index ebca3937b..a0dd573ba 100644
--- a/content/articles/minimalism.md
+++ b/content/articles/minimalism.md
@@ -5,8 +5,6 @@ location: San Francisco
 hook: Practicing minimalism with the lofty goal of total
   ephemeralization to build coherent, stable, and operable
   stacks.
-hook_image: true
-twitter_image: true
 attributions: Photographs by <strong><a href="https://www.flickr.com/photos/i-am-mclovin/14601998033/">Ben Harrington</a></strong> (SR-71), <strong><a href="https://www.flickr.com/photos/learnscope/5032942270/">Robyn Jay</a></strong> (embers of a burning fire), and <strong><a href="https://www.flickr.com/photos/alamin_bd/22969073683/">Md. Al Amin</a></strong> (boat and sky). Licensed under Creative Commons BY-NC-ND 2.0, BY-SA 2.0, and CC BY 2.0 respectively.
 ---
 
diff --git a/content/articles/newsletters.md b/content/articles/newsletters.md
index 0c488d3f1..61d26054f 100644
--- a/content/articles/newsletters.md
+++ b/content/articles/newsletters.md
@@ -3,8 +3,6 @@ title: "Pseudo-HTML and Pidgin CSS: Building an Email Newsletter"
 published_at: 2017-08-02T14:52:31Z
 hook: Building a toolchain for sending a newsletter, and
   the dismal state of HTML and CSS in email.
-hook_image: true
-twitter_image: true
 ---
 
 After a recent trip to Portland, I decided to try writing a
diff --git a/content/articles/page.md b/content/articles/page.md
index ec6a439c8..d9ec134c9 100644
--- a/content/articles/page.md
+++ b/content/articles/page.md
@@ -3,8 +3,6 @@ hook: How the page almost transitioned successfully to the
   digital world, but is in decline in new media. The
   lessons that we can learn from this age-old design
   element, and why we should hope for its re-emergence.
-hook_image: true
-twitter_image: true
 image: "/assets/page/page.jpg"
 location: San Francisco
 published_at: 2014-01-26T18:56:46Z
diff --git a/content/articles/postgres-atomicity.md b/content/articles/postgres-atomicity.md
index a7cfe356a..0a5fadd8d 100644
--- a/content/articles/postgres-atomicity.md
+++ b/content/articles/postgres-atomicity.md
@@ -5,8 +5,6 @@ location: San Francisco
 hook: A dive into the mechanics that allow Postgres to
   provide strong atomic guarantees despite the chaotic
   entropy of production.
-hook_image: true
-twitter_image: true
 hn_link: https://news.ycombinator.com/item?id=15027870
 ---
 
diff --git a/content/articles/postgres-reads.md b/content/articles/postgres-reads.md
index 6df94eb2b..44bea2175 100644
--- a/content/articles/postgres-reads.md
+++ b/content/articles/postgres-reads.md
@@ -6,8 +6,6 @@ published_at: 2017-11-17T22:02:56Z
 hook: Scaling out operation with read replicas and avoiding
   the downside of stale reads by observing replication
   progress.
-hook_image: true
-twitter_image: true
 hn_link: https://news.ycombinator.com/item?id=15726376
 ---
 
diff --git a/content/articles/redis-streams.md b/content/articles/redis-streams.md
index c85759f6b..8a9cdf200 100644
--- a/content/articles/redis-streams.md
+++ b/content/articles/redis-streams.md
@@ -5,8 +5,6 @@ location: San Francisco
 hook: Building a log-based architecture that's fast,
   efficient, and resilient on the new stream data structure
   in Redis.
-hook_image: true
-twitter_image: true
 hn_link: https://news.ycombinator.com/item?id=15653544
 ---
 
diff --git a/content/articles/stripe-running.md b/content/articles/stripe-running.md
index 3cc43491e..d2502c981 100644
--- a/content/articles/stripe-running.md
+++ b/content/articles/stripe-running.md
@@ -3,7 +3,6 @@ hook: Crunching running data with prepared statements in Postgres.
 location: San Francisco
 published_at: 2015-10-24T20:55:32Z
 title: Running at Stripe
-hook_image: true
 ---
 
 One pleasant surprise of Stripe's internal culture was the existence of a
diff --git a/content/articles/webhooks.md b/content/articles/webhooks.md
index e98bbeceb..75054ea6a 100644
--- a/content/articles/webhooks.md
+++ b/content/articles/webhooks.md
@@ -6,8 +6,6 @@ hook: When it comes to streaming APIs, there's now a lot of
   great options like SSE, GraphQL subscriptions, and GRPC
   streams. Let's examine whether webhooks are still a good
   choice in 2017.
-hook_image: true
-twitter_image: true
 attributions: Thanks to <a
   href="https://twitter.com/spencercdixon">Spencer
   Dixon</a> for review.
diff --git a/content/articles/x100s-hack.md b/content/articles/x100s-hack.md
index f45f30535..a80f3c156 100644
--- a/content/articles/x100s-hack.md
+++ b/content/articles/x100s-hack.md
@@ -4,8 +4,6 @@ hook: If you find that the price tag for a Fuji-official adapter ring for the X1
 location: San Francisco
 published_at: 2014-08-03T16:50:19Z
 title: A Cheap X100S Filter Ring Hack
-hook_image: true
-twitter_image: true
 ---
 
 The [official Fujifilm X100/X100S 49 mm adapter ring](http://www.amazon.com/Fujifilm-AR-X100-Adapter-Ring-49mm/dp/B004MME69S) which allows you to mount extra filters onto your lens will run you about $40, which is a little steep considering that its entire role in life is to act as an expensive spacer.
diff --git a/content/drafts/microservices-and-the-monolith.md b/content/drafts/microservices-and-the-monolith.md
index c92851169..f7027ff5c 100644
--- a/content/drafts/microservices-and-the-monolith.md
+++ b/content/drafts/microservices-and-the-monolith.md
@@ -3,8 +3,6 @@ title: Microservices and the Monolith
 published_at: 2017-01-05T16:41:25Z
 hook: Microservices may be out of vogue, but we should be
   wary of overcompensation.
-hook_image: true
-twitter_image: true
 ---
 
 About three years ago, the idea of a service-oriented
diff --git a/content/drafts/ruby-scale.md b/content/drafts/ruby-scale.md
index e49f5e12b..1044c42c2 100644
--- a/content/drafts/ruby-scale.md
+++ b/content/drafts/ruby-scale.md
@@ -4,8 +4,6 @@ published_at: 2017-04-18T14:23:28Z
 location: San Francisco
 hook: The challenges of scaling and operating a big Ruby
   codebase (that are not related to performance).
-hook_image: true
-twitter_image: true
 ---
 
 Ruby is a beautiful language. Speaking from experience,
diff --git a/content/fragments/airpods.md b/content/fragments/airpods.md
index 5041de27a..abb1d3b10 100644
--- a/content/fragments/airpods.md
+++ b/content/fragments/airpods.md
@@ -2,7 +2,6 @@
 title: AirPods
 published_at: 2017-03-29T14:44:33Z
 image: /assets/fragments/airpods/vista.jpg
-twitter_image: true
 hook: I'm happy to be cheering from the bleachers as Apple
   makes their first home run in years.
 ---
diff --git a/content/fragments/ipad-mini.md b/content/fragments/ipad-mini.md
index 0cb680a16..34379944a 100644
--- a/content/fragments/ipad-mini.md
+++ b/content/fragments/ipad-mini.md
@@ -2,7 +2,6 @@
 title: The iPad Mini
 published_at: 2016-06-12T22:26:17Z
 image: /assets/fragments/ipad-mini/vista.jpg
-twitter_image: true
 hook: An ode to one of my favorite Apple devices.
 ---
 
diff --git a/content/fragments/ivy.md b/content/fragments/ivy.md
index e01d72374..8e71d1b3c 100644
--- a/content/fragments/ivy.md
+++ b/content/fragments/ivy.md
@@ -1,7 +1,6 @@
 ---
 title: Ivy
 published_at: 2016-08-24T03:12:31Z
-twitter_image: true
 image: /assets/fragments/ivy/vista.jpg
 hook: Stripe's new home in SOMA.
 ---
diff --git a/content/fragments/monkeybrains.md b/content/fragments/monkeybrains.md
index 00ce9b1af..8629db7e0 100644
--- a/content/fragments/monkeybrains.md
+++ b/content/fragments/monkeybrains.md
@@ -2,7 +2,6 @@
 title: MonkeyBrains
 published_at: 2016-01-23T01:15:58Z
 image: /assets/fragments/monkeybrains/vista.jpg
-twitter_image: true
 hook: A very brief review of the local San Francisco ISP.
 ---
 
diff --git a/content/fragments/sprawl-blues.md b/content/fragments/sprawl-blues.md
index fdfc04586..3dea6d7e1 100644
--- a/content/fragments/sprawl-blues.md
+++ b/content/fragments/sprawl-blues.md
@@ -2,7 +2,6 @@
 title: The Sprawl Blues
 published_at: 2016-01-03T22:18:36Z
 image: /assets/fragments/sprawl-blues/vista.jpg
-twitter_image: true
 hook: On sprawl and commute times in North America.
 ---
 
diff --git a/content/fragments/wgt-2015.md b/content/fragments/wgt-2015.md
index d5f91107f..1a676d74a 100644
--- a/content/fragments/wgt-2015.md
+++ b/content/fragments/wgt-2015.md
@@ -2,7 +2,6 @@
 title: WGT 2015 Abstract
 published_at: 2015-05-29T13:34:59Z
 image: /assets/fragments/wgt-2015/vista.jpg
-twitter_image: true
 hook: A whirlwind tour of Wave-Gotik-Treffen 2015.
 ---
 
diff --git a/content/fragments/your-name.md b/content/fragments/your-name.md
index 457fddb2b..d1a3dde20 100644
--- a/content/fragments/your-name.md
+++ b/content/fragments/your-name.md
@@ -2,7 +2,6 @@
 title: Your Name
 published_at: 2017-04-11T01:26:59Z
 image: /assets/fragments/your-name/vista.jpg
-twitter_image: true
 hook: A short review of Makoto Shinka's latest animated
   film.
 ---
diff --git a/views/articles/index.ace b/views/articles/index.ace
index 8ba057899..72b465c8a 100644
--- a/views/articles/index.ace
+++ b/views/articles/index.ace
@@ -25,9 +25,9 @@
               ul
                 {{range .Articles}}
                   li
-                    {{if .HookImage}}
+                    {{if .HookImageURL}}
                       a href="/{{.Slug}}"
-                        img src="/assets/{{.Slug}}/hook.jpg" data-rjs="2"
+                        img src="{{.HookImageURL}}" data-rjs="2"
                     {{end}}
                     .title
                       a href="/{{.Slug}}"