Testing an image directory for hidden rars?

How would someone go about quickly testing each and every image to see if it had a rar or any other file hidden inside of it? What language would be best for doing this, if a tool isn't already available?

so with cygwin after downloading it do I just type in grep 'Rar!' *.jpg and its suppose to pull it up ? because its not working for me it tells me grep: *.jpg: No such file or directory.