>>105811934
I'm not testing modern formats, just plain old Webp and the more ancient JPG image format.

I got a score of 6.1268320084 for the 62KB JPG in >>105810672
vs a score of 8.4359798431 for the 24.6 KB Webp in >>105809883

I would definitely not rate the JPG as better than the Webp so I can't-believe-it's-not-butter is an utter failure like SSIM and PSNR for cartoon images as well. I'm not giving up yet thoughbeit.