What sort of error did you have in mind? (When you upload the image, on the image description page [probably the best bet], when you are previewing a page that is going to include said image, directly where the image is included, something else?)

Most practical I would imagine would be on the image description page, right where the "Obesity_state_level_estimates_1985-2010.gif ‎(612 × 451 pixels, file size: 567 KB, MIME type: image/gif, looped, 26 frames, 26s)" line is.

Commons has a manually populated category:
http://commons.wikimedia.org/wiki/Category:Animated_gifs_exceeding_the_12.5MP_limit

An automatically populated category would be nice.
The default name might be
Category:Animated gifs exceeding the scaling limit

See also related bug 23063

Gerrit change 20662 introduces a warning on image description pages if we can't animate thumbnail (That includes APNG and animated SVG's as well).

An automatically populated category would be nice.
The default name might be
Category:Animated gifs exceeding the scaling limit

How much is this wanted. The parser is kind of separate from displaying the image, so I'm not sure what a clean way of adding the category would be.

An automatically populated category would be nice.

How much is this wanted.

It doesn't seem important if the image description page displays a warning.

M8R-udfkkf wrote:

I would support an image description warning like what Bawolff suggested.

(In reply to comment #3)

Gerrit change #20662 introduces a warning on image description pages if we can't
animate thumbnail (That includes APNG and animated SVG's as well).

This is now merged.