Check to see whether they have been dumped in a version set. You should see a right pointing arrow on the thumbnail. Click on it to expand the set.
If you find the batch inside a version set it is possible to select them all and remove them so that they are treated as independent images.
Thanks for the reply. My Image wasn't in a version set however. I scanned a new photo which was successsful. I then scanned a second photo different from the first, which failed. I think possibly the software for my HP scanner is at fault, since it always names the scans as image1.jpg. It doesn't give an option to increment successive scans to a different name which probably caused the problem.