I never was a great fan of programs that would hide files or information but I can see that some people might find this kind of tools useful. I can think of several reasons why someone would want to hide files in pictures; maybe it is because a file needs to be sent by email and no one that would intercept the email would find the file or a way to bypass a filter easily.
Hide in Pictures is one of those tools that lets you hide files of in bmp and gif images. The file size has to be in relation to the size of the image which means that you can’t add a 700 megabyte avi file in an 2k gif image. Double-clicking the image displays it as usual and normally most users would not suspect that a file is hidden inside the image. Bmp files seem to be better suited for this because they are usually larger than gifs by default.