DeJPEG is a tool which can extract the JPEGs from any file, and save them as separate images.
You might have a PDF or DOCX file, say, with a lot of embedded JPEGs. Manually extracting them would be time-consuming, even if you had the right software - and that's where deJPEG comes in. Just point it at your PDF, click "Analyse file", and the program will examine the source file, saving any JPEGs it finds in the same folder.
Our first problem with this approach is it's a little too simple. You can't define an output folder, for instance - any JPEGs are automatically saved to the same folder as the source file. And you can't specify any pattern for the output file names. They're always "image1.jpg", "image2.jpg", "image3.jpg" and so on.
Another complication is that the files aren't always what you'd expect; we found some were distorted in some ways, others didn't appear to be regular JPEGs at all.
Still, one significant plus for the program is it doesn't care about the source file format. It doesn't matter if you give it a Word document, a spreadsheet, a database or anything else. Whatever the file type, deJPEG will just scan through its contents, extracting anything which looks like a JPEG.
And while the program regularly failed to deliver in our tests, on many other occasions it worked perfectly. So if you ever need to extract images from a file or document, we'd grab a copy anyway - one day it just might prove very useful.