I tried to wait for it to finish, but after a couple hundred more repetitions of JzH it just stopped abruptly without a closing parentheses, so I think I’ve been had.

I can't get it to decode, even after correcting the base64 padding. Firefox just shows the broken image icon. My image viewer throws out the glorious log message Image format is actually "png" not "png", along with a bunch of checksum errors.

I guess, the checksum can't be correct when it's cut off, but none of my image viewing/editing software wants to look past that.

In a hex viewer, it looks like this:

Compared to a normal PNG:

I don't know the PNG spec by heart, but I guess, it doesn't look completely off the rails before it goes there...

It's possible that the first part is, but it didn't finish the image.

It used to do this all the time a few months ago. The links never worked. Eventually I got bored of asking it.

It's not an image. It's a string of text designed to look like a link to an image. But it isn't a link to an image. You'll get a 404 if you try to use it.