Digital Inspiration has a pretty cool post that walks you through how to hide documents, such as a text file or Excel spreadsheet, in an image file. If someone tries to open the image they won’t notice anything different because they will see an un-distorted picture that appears to be normal (except maybe for the file size).
The main thing that you need to do is use the following text at the command prompt:
copy /b imagename.jpg + documentname.xls generatedimage.jpg
That code is assuming that the files being used are located at the root of your drive. To “recover” the document you just need to change the extension back to the original file type.
This almost reminds me of those book safes (pictured above) because it may not be the easiest thing to find but once you do find it the contents are easy to get.