Deleting merely removes the reference to the data, though the data is still there. This is how recovery programs work -- by searching a drive for identifiable data, such as pictures. The limitation is that once you write anything new it can write overtop any free space, such as previously deleted files.
As an extreme example, if you deleted a bunch of pictures and then filled the drive with new data, *all* of those pictures will be impossible to recover (the pictures were overwritten). The more writing you do since you deleted, the more chance of something being overwritten.
So yes, if it's been a few years and you've been using this SD card... those images are likely long gone. If you've ever filled the card to capacity since deleting, the old image data is completely overwritten.
