printing photos from Photos in iMac

You can copy the image with the (I think) image->duplicate it might be in the file menu or in the right(option) click menu.

Then you can select them both.

You can delete the duplicate when you are done printing.

As Keith says, duplicating (command-d) the picture is the answer. A caution, however:

The duplicate is indistinguishable from the original--same date, same keywords, everything. Except, the duplicate in not in any albums other than the one you duplicated it in. So if you delete (command-delete) the wrong one, then while you will still have the picture (copy), it won't be in the albums you expect. You may want to identify the duplicate by adding a keyword, maybe "duplicate," so you will later be deleting the right one.

After duplicating the photo as Keith mentioned, select both imagers, type Command+P and do the following: