How do I move a photo from Photoshop back onto a Flash drive

Can you please explain your problem in more detail?  What OS and version of Elements are you using?

Are you talking about a photo that is in your Organizer catalog? 

Was the photo originally imported from the flash drive and deleted from there?  If the file was in fact imported from the flash drive, it should have been copied to your hard drive.  If that is the case, select the photo in the Organizer grid and click on the Location link found in the Information panel on the right.  This will open up an Explorer/Finder window and you can simply copy and paste the file from your hard drive to your flash drive.

If you want to place your Organizer catalog files onto a flash drive instead of a hard drive, we need to have a whole different discussion.