Deleting or formatting won't make the data in memory card erased permanently.
Those lost pics are still stored on the memory card, it's just invisible or inaccessible. Only the FAT or NFTS table is erased (the information about where those data were saved), but the real data are still intact there in sectors of the hard drive.
So as long as those photos are not overwritten by new pictures, it's highly possible to recover them. And the MOST Effective way is to rely on some format recovery
Try Asoftech Photo Recovery program, which can recover pictures after deeply scanning the memory card to look for lost pics you accidentally deleted or formatted.http://www.asoftech.com/apr/
Here's a format memory card recovery tutorial