First Post so excuse me if I use the wrong terminology. I’ve been dragging and dropping artwork files from Windows File explorer (on one monitor) onto MP3TAG on another monitor (onto the Tag Panel on the left side of the screen). Sometimes it adds to the existing artwork, and sometimes it replaces what is there. I think I discovered that IF the existing artwork (among multiple selected files) have identical quantity, size, and contents (of artwork) than the new artwork ADDS to the existing. IF the artwork is DIFFERENT (among the selected files), that the new artwork(s) REPLACES the existing artwork. Is this correct? Is there a way to select the behavior somewhere (to ALWAYS ADD, or REPLACE)?
If you press the Ctrl key before you release the dragged picture on the Tag Panel, you should see a (small) + sign in the right corner of your cursor-arrow.
This indicates that the picture will be ADDED in addition to the existing ones.
It will also be added to the different existing pictures.
Example:
+ sign (=ADDING) pressing the CTRL key during drag & drop:

Thanks. How simple! Wish I would have tried that. Or, perhaps I should have tried reading the documentation more.