Photos can be deleted from the list of photos by selecting the photo name in the list in the main window and then clicking the 'Remove Picture' button (multiple photos can be selected and deleted).

PhotoInfoEditor will NOT delete your original picture files, it only removes the photos from the list. Once a picture has been removed from the list it may be a good idea to save the list by using either command-S or using 'Save Data' from the 'File menu'.