How did you back them up? I am assuming you mean the SD card, not a chip. You can't put photos and videos on a SIM card, that just gets you service. Data would go on an SD card.
If they were erased from an SD card, it is going to depend on how they got erased/deleted. You may be able to connect the SD card to a computer and run data recovery software to see if you can get back some of the lost data.
Now if you had the phone synced to your gmail, then you should have copies of all things you synced in that account.