You can try either a free program such as "recuva" or send the hard drive in for professional services. The second option would be expensive and neither would guarantee success. Recovery depends on whether or not the areas of the disk that contained the desired data were overwritten during the restore process. If the pictures were in a physical area of the disk outside that used during a factory restore, you might get lucky.
I have an HP notebook running Windows 7 Home Premium. I restored it to the factory settings default and I accidently lost my son's pictures. He doesn't have them backed up. Any idea how I can retrieve them?