Although this might vary from case to case with the specific circumstances, the basic way to argue for the exclusion of such evidence is to claim that it is not trustworthy.
First of all, it is very easy in today's world to "doctor" photographs and video recordings. A defense attorney could argue that such evidence might not truly show what it purports to show because it might have been altered.
Second, it is quite possible that a photograph (in particular) or even a video recording might not show the totality of the circumstances surrounding what has happened. A photograph shows one moment in time without showing anything about what happened just before or even one moment after. A video recording is also limited in time. It also may not have high quality audio and the picture itself may not be completely clear. If such things are admitted as evidence, juries may tend to give them more weight than they should be given due to their limited nature.
Therefore, a defense lawyer could argue that such evidence is too prone to being altered and is too likely to tell only one part of a given story. Because of this, the lawyer could say, the evidence should not be admissible.