Hi,
If you just want to preserve the information on the backs of the photos, you can scan in the photo and import it into the Photos app. Then do a Control-Get Info on the photo. A box will appear that will let you add a description. Type in the content of the handwriting that is behind the photo. You can type in a very long description. Then, whenever you do a Control-Get Info on the photo the box will pop up with your description on it.
If you want to preserve the actual handwriting itself, you can photocopy the back of the photo and then scan in the photo together with the photocopy of the reverse side. The scanned composite will display the photo and the handwriting. Once the composite is imported into the Photos app you can always make a duplicate of the composite and then crop out the handwriting to edit or make a print of just the photo. Or, you can edit and/or print out the whole composite if you want.
The only other way that I can think of is to scan in the photos and the reverse side separately and keep them both together in the Photos app, perhaps assigning keywords to them or putting them in separate albums.
-- Rich