Thank you for your answer. I was confused by the documentation that states:
Use AsString property to read/set the blob content as string
If you want to work with the blob content as string, you can just use AsString property for that:
Customer1.Photo.AsString := 'Set string directly to the blob';
I expected Aurelius to take core of the conversion from the native string to whatever is supported by the underlying storage system - in particular since none is required in this case.