How to easily tell which file/asset is not being used in any compositions?

Is there a way in AE to easily tell which file/asset is not being used any of the compositions in a project? I'm making a slide show and I like to know which image has not been used in the current project's compositions so that I can use that image in another slide show project. It's a pain to go through each compositions/timeline and determine which image hasn't already been used and manually moved those images to another another project.