Well, if you had the phone synced to say a Google account, your photos may be there. If not, and you didn't back them up to say a computer or a cloud account, they are pretty much gone.
That said, there are things you can try to get them back, but there are no guarantees it will work.
There are a few apps/programs out there that 'may' be able to help you recover the data.
A few of the programs you could try would be... DiskDigger, MobiSaver, Android-Recovery and Tenorshare. They are all data recovery apps/programs. There are many others out there, so check around and see which you would rather try. There is also one called RECUVA, that I have heard is free, which you could try.
One important note though, most of these programs are...