A way to indicate within the HTML <img> tags the limitations on image quality

[RachelComerford]

Sometimes the quality of an image "is what it is". The book may have been published long ago, the original may be a copy from newsprint, the image may be historical. It would be great if we had a way to indicate this within the content so that reading systems could interpret it to know when to warn a reader that this isn't going to enlarge all sharp and clean and it's not because anyone is holding out on better quality.

Marketplace Impact
There is currently one retailer requesting this and it would be good to find a standard way to address.

Possible Tech Impact
We need to consider whether this has any bearing on accessibility features for ebooks or a use for these readers, who might also benefit from knowing that a historical or space image is blurry.

@liisamk There is also the possibility that this could just be something like "Historical Images throughout this book are presented at the highest resolution possible." and it would just be a best practice.

@TzviyaSiegman use details element in HTML
https://www.w3.org/TR/html52/interactive-elements.html#the-details-element

[JayPanoz]

Philosophically, I would perhaps extend this issue to a more general “hints for images.”

We’ve explored that super early in ReadiumCSS but for night mode (e.g. a hint that tells the RS it should invert the image in night mode, if possible) but to no success.

For this case, there’s a precedent i.e. gaiji images, with one major RS using class and a custom meta (opf).

The trickiest part is that “hints” would be defining RS behavior.

If the RS were entirely in charge or an author had to implement it on her/his side, custom data-* attributes would probably be used there (i.e. custom data private to the page or application, for which there are no more appropriate attributes or elements).

So what would be the more appropriate attribute there?

At first I though width and height could be used by the RS (zooming, which can be relative depending on the screen size/resolution) but that can’t obviously work for blurry or pixelated images.

Pinging @danielweck and @HadrienGardeur since we discussed zooming images at some point in R2.

[llemeurfr]

IMO this is difficult to add to "best practices", more a sort of affordance the content would provide to reading systems. It will be difficult to detail such affordance but not include it is the standard. And including it in the WP standard makes no sense, as it is a Web-wide issue.