It's easy to make a file that both a valid image and a valid zip file, because zip readers start from the end-of-central-directory at EOF and most other things start from a header at the start of the file. Many such images included a winrar icon.
There might have also been some steganographic images, but I know for sure I saw several of the image+archive kind around then.
There might have also been some steganographic images, but I know for sure I saw several of the image+archive kind around then.