This could be painful

I agree with Jimmy. This wholly depends what type of factory reset was carried out.

If it was a 'repair' type of install, then the pictures may still be on the hard drive in some reserved folder somewhere. But if this was a complete reinstall back to factory default, then the disk has been wiped and those files are gone.

In the latter case you will need to make a decision. If you want to attempt recovery of the picture file fragments then the advice is, stop using this hard drive completely, and take it or send it to a Data Recovery service. Even though the disk has been formatted it is possible that some of those image files can be recovered. But the more you use the hard drive the more you risk over-writing these file fragments with new data.

As Jimmy says, this is likely to be expensive.

Mark