Do files on USB drive leave any trace on iMac (macOS Sierra)? I'd like to know if I look at files (specifically jpegs) stored on a usb drive without opening them, will they leave a trace on the iMac I'm putting the USB into? 

Bascially, if I plug in a USB and don't actually open the jpeg files (eg. using preview) but only look at them as thumbnails in the finder folder, will they still leave a trace on the computer? 

Also, if I move the jpeg files from one folder to another on the same USB drive, or from one usb drive to a different one (both plugged into the same iMac), does that also leave any trace on the computer?

I want to know if anyone else accessing the computer will be able to see any trace of the jpeg files after I've removed the thumb drives. And if so, is there a  way to delete it?
If you open a folder with files residing on an external drive, thumbnails will be created on the boot drive depending on the file type and the installed QuickLook plugins.

The previews, metadata and file paths are stored in SQLite database files deep inside the var folder in the com.apple.QuickLook.thumbnailcache folder. The path to this folder contains arbitrary folder names.

With the proper commands the preview pics can be extracted from the database.



To remove the pic previews and other data you would have to delete the content of the folder.

Related links: 


View thumbnail cache in OS X
Collecting Quick Look Data From a Live macOS System