Image –› Code

So,  I'm curious about how things like the 4chan.hta were made. If you're not familiar, it's basically an image file that when saved as an hta epuld execute some entertaining code. The only way I could think it'd work is if it the text was converted to binary and then that was used for the image. So any ideas?

Considering 4chan strips everything after the end of the actual image now, would there be any way to have an image that isn't just snow execute?