FYI - CM / 8ch is NOT altering originals.
It's CloudFlare. When snagging the originals gotta make sure to bust the caching front ends.
A simple "?13245123" or something random at the end of the filename will help.
Also: curl -H -vvvv is your friend.
Finally: the jpeg header hex signature isn't a 100% guarantee it's PixelKnot. All it says is that the image has been through some sort of image editing tool.
The more you know…