Cannot figure why SEO would differentiate between image file format. In any case, images should all have alt="alternate text" attribute, which is what would influence page "content" rating.
Have not gotten into SVG or APNG. Basic Web image formats are JPEG, GIF, PNG.
A GIF image is a GIF image whether animated or not. SEO crawlers don't "see" the difference; they just read the ALT text. (I think.)
JPEG's are for tonal images (photos, gradients), GIFs for flat 256 colors and transparent ares. PNG-24 offers shades of transparency.