It doesn't help with determining how Alice took the photo - with her camera or with her version of Stable Diffusion. Only that at t=0 Alice uploaded the hash of the photo she had before it.
What your parent described is a type of trusted timestamping and one doesn't need blockchain to implement it.
For instance, Alice is accused of a crime that happened a month ago. There exists photo / video of Alice that is attested this way proving she hasn't committed the crime, and this is taken by Bob who seems to be an uninterested third party.
It doesn't preclude criminal Alice from setting up this situation in advance given her intent to commit a crime, but it does seem to make it way harder.