Animated GIFs are hit or miss

[shiimizu]

Some GIFs aren't converting to the correct images to get the matching checksums.
This can be seen with running tg on dance.gif.

Some leads

For some image types, the presence of channels and bits values can be a bit confusing. As an example, GIF always uses 3 channels per pixel, but the number of bits per pixel cannot be calculated for an animated GIF with a global color table.
~ getimagesize manual

• ext/standard/image.c (PHP)
• gd_gif_in.c

Something related to colors or compression for animated GIFs seems to be going on.

[shiimizu]

Fixed in b122b7f