I've been trying to burn backup disks of my photos. However, I have tried to burn the same group of photos three times and each time it fails verification due to "sector unreadable." A surface scan of the burned DVD reveals bad blocks.

I have burned other groups of photos fine using the same drive and media.

I'm using Toast 7.1.2 on a G5 running 10.4.11. I'm using Taiyo Yuden DVD-R (4.7GB).

I figure there must be some problem with one of the files I'm trying to copy. Is there any way I can narrow it down and find the offending file? Would copying all of the photos to a different disk and then trying to burn from there help?

You may have a batch of defective discs. The errors that sector is unreadable and bad blocks indicates a media problem. Before spending time trying other solutions I'd try with a different spindle of another brand of discs.