I think you can guess that part. I doubt a current LLM can create a valid PNG, even if it's just a 1x1px one that has been created before. This is partially because PNGs have a checksum and the LLM has definitely not seen enough PNGs in base64 to figure out the algorithm, and is not optimized to calculate checksums. In fact, I analyzed the image and the image header checksum is wrong even though the header makes sense (was likely stolen). Also, it gets penalized for repetition, which occurs a lot in image headers.

AFAIK, the smallest valid image you see mentioned on the web is a 35-byte transparent pixel GIF, and the smallest PNG is a black pixel with 67 bytes:

data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEAAAAALAAAAAABAAEAAAIBAAA=
data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQAAAAA3bvkkAAAACklEQVR4AWNgAAAAAgABc3UBGAAAAABJRU5ErkJggg==

Testing rendering: , , another 67-byte PNG but 8 px wide: , or 1 gray pixel: , or a green one:

The article + the generator

I think it was one first and then the other