The issue is cost. Proving that an image is or isn't photoshopped isn't all that difficult/expensive. Anyone well versed in digital imagery can use basic tools to expose 99.99% of photoshopped images. But moving pictures are different. Due to compression artifacts and the overall lower quality of each frame there is much more room for opinion. An answer one way or another may be possible but it will be a much greater and more expensive battle of experts.