Is your feature request related to a problem? Please describe.
This issue is related to PR #287 where it is difficult to tell when an image was last updated and to ensure that you're not looking/querying against stale data.

Describe the solution you'd like
I'd like this to be implemented as a new metric, matching similar labels to that of the image,

This could be implemented automatically, every time the metric value is set/updated.. with a time.Now().Unix() and implemented as a Gauge datatype.

Message from the maintainers:

If you wish to see this enhancement implemented please add a 👍 reaction to this issue! We often sort issues this way to know what to prioritize.