Open Photo gallery

Is there a filename under the photos? If so you can do a search for one of the names in Windows explorer. Most likely, all of the photos are in the same directory. Once you have located them, you can select and delete them. If no filenames are displayed, try right clicking on one of them and checking properties if a menu pops up. It may list the target file for the thumbnail photo. This will then allow you to locate and delete them.