On Windows it won’t let you delete an image (in basic cards not image occlusion) once you add the image attachment into the card whether front or back. I tried selecting it and right clicking but there’s no delete option I also tried pressing backspace or delete on the keyboard but they don’t delete the image either. You end up having to delete the whole card and restart if you added the wrong image.
You need to put the cursor into the field (or select the image like a piece of text there) before pressing the keys. If it doesn’t work, that sounds more like a bug than a problem with card design, in which case you should probably go through the troubleshooting steps first and reply with the results.
As a workaround you can try expanding the field using the <> button at its top-right corner and removing the image from the source code.