This is terribly antithetical to the principles of the Internet, but... the interlacing is very clever, even though it doesn't look right on my browser (shimmering black).

I could solve the invisible wall demo trivially (Inspector > Network > cat.png -- this also worked for the interlacing demo). The encrypted demo took a few more seconds: Inspector > Delete transparent.jpg > Right click canvas > Save Image As.

If the interlacing one was using the encrypted image, and if its JavaScript was obfuscated (so I couldn't easily determine the encryption algorithm), I could (kinda) solve it by pausing script execution in Firefox's debugger, then changing the opacity on both canvases to 1 - then taking a screenshot of the picture. But this is harder to achieve reliably for scaled-down images.

Mozilla should start thinking about ways to help users fight this kind of bullshit; e.g. having right-clicks apply to highest opaque image or canvas, ignoring any transparent elements.