Add a linter to check the images' alt text

[arnaucasau]

In order to meet the IBM Accessibility Requirements for the API docs, we need to ensure that all images have appropriate alt text so that users can understand any meaningful visuals. The alt text should serve the same purpose as the images on the page, conveying the same meaning rather than describing visual characteristics. In addition, if an image contains important words for understanding the content, the alt text should include those words as well.

This PR adds a linter to check that all images have alt text. The current invalid images, if any, have been included in an allowlist that will help us to not break CI before the text is added.

If the script detects an image without alt text, it will show an error indicating the file where the image is located and the line where we are using a sphinx directive like .. image:: or .. plot:: that generates an image. Example:

💔 Some images are missing the alt text

Errors found in qiskit_ibm_runtime/fake_provider/__init__.py:
- Error in line 34: .. plot::

Alt text is crucial for making documentation accessible to all users. It should serve the same purpose as the images on the page, conveying the same meaning rather than describing visual characteristics. When an image contains words that are important to understanding the content, the alt text should include those words as well.

To fix the error, the :alt: [Your text here] option must be added under the lines indicated in the error messages. However, If the .. plot:: directive is used, but no image is generated, you can use the option :nofigs:.

[coveralls]

Pull Request Test Coverage Report for Build 12259315108

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 12026078671:	0.0%
Covered Lines:	577
Relevant Lines:	577

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💛 - Coveralls

[mrossinek]

The current invalid images, if any, have been included in an allowlist that will help us to not break CI before the text is added.

I don't understand this. If all current images can be left as-is without any alt text, is this a high priority or not?
If it is a high priority, adding alt text to the existing images should be, too, and merging of this PR was pre-maturely.
If it is not a high priority, why did this PR have to get merged before adding alt text to those images?

Given the state of it now, please open an issue (or a PR) to ensure that alt text does get added to the currently allow-listed images. Without a tracking issue, I don't see anyone coming back to this in the future.

[Eric-Arellano]

Hey @mrossinek , pardon me merging before you intended!

It is high priority to fix - Becky has been making good progress on ensuring all 9 APIs on docs.quantum.ibm.com have alt text. She hasn't gotten to this repo yet, but plans to as part of Qiskit/documentation#2408. It's a top priority for the docs team.

*We wanted to land this in the meantime for two reasons:

1. Ensure no new regressions are introduced
2. Make it easier for Becky to find the violations and fix them

[mrossinek]

No worries at all, I'm glad this is moving along while I'm busy elsewhere and did not have time to review 👍

Simply wanted to follow-up on this, as it caught my eye and I didn't see any discussion around potential follow-ups 👍
Seems like you have that all laid out though 🙂