See attached image.
Taken from:
https://webassembly.sh/?run-command=wapm%20install%20caputomarcos/rust-example@0.1.0

Also saw a similar issue while trying to upload images to the
merveilles.town Mastodon server. The image would have similar diagonal
lines that were all of the same maybe 2-4 colors and each about 1 pixel
wide.

I haven't touched JavaScript and the canvas element in a looong time,
so I might be wrong, but my suspicion is that rendering images to it is
what causes the issue.