How will you be aware of it? And what prevents someone from tweaking one pixel by one bit, changing the hash of the new image?
So they wouldn't necessarily naively hash an image file, but they could possibly create a hash from features that are extracted from the image and remain consistent even after manipulation or transformation.
Or they could hash the original bits in the file naively then insert that hash into the original image as a digital watermark that would survive manipulation of the image.
I suspect this would be solved by visually comparing the two images and noticing that they are one in the same. Than you can just see which had their hash published on the block-chain first to see which is the real one.
Just identifying the images are the same doesn't prove which was the original though. The hashes being publicly available is the key, because you can easily tell which came first.
Hashes don't verify the date that something was created. The blockchain provides a date for the hash, but it provides no guarantee that the hashed item didn't exist long before when it first appeared on chain. If I simply modify the image metadata to say that my knockoff photo was taken at an earlier date and flip some bits, I can still claim that mine is the original and that I didn't submit it to the blockchain when I created it.