the upper line of Sandisk (not Scan Disk) cards come with a software that allows you to retrieve lost images but if you don't have any of those cards I recommend gettingactive@undelete
a very very powerful program that finds anything you ever recorded on any type of memory, as long as it hasn't been rewritten. I have used it for years, it get regular updated, I think it's the most powerful data retrieval software in the market.
I think everybody should have it. It costs $39.99 which is nothing for what you get. You can also download a demo to try it out. Make sure you don't save reetrieved data on the same device.