How can I get my pictures back from when i backed up my iphone?
it sounds like you have a recent backup -- so that's great news.  don't let anything over write that before you can extract your files from it.

in this case, utilities like  will let you parse through the backup files/folders and get to the photos.  these guys have a free one i just did a quick test with, and it is simple once it reads the backups and parses through it:

http://www.easeus.com/data-recovery/iphone-data-recovery/extract-iphone-data-from-itunes-backup.htm

let us know how it goes.