The 64-character code is the sha256 hash of the image.
That means that it can't have any message inside it because it's completely determined by the contents of the image.
The output of a cryptographic hash algorithm is completely random and small changes in the file produce completely different hashes with no relationship to one another.
So there's no way to tweak the file to get a specific hash that you want which could say something that you want it to say.
There is no information in the stringer at all, other than a summary of information from the image.