Run the image through SHA-2.
Eliot should run the image through SHA-2.
The SHA-2 hash function family consists of four algorithms, the most common of which are the 256-bit and 512-bit varieties. Hashes are used to prove integrity of data and images.
Compressing the image would only decrease the storage space needed for the image; it would not ensure integrity.
Running the image through AES-128 would encrypt it, ensuring confidentiality but not integrity.
Making a duplicate would allow for availability but not integrity; in fact, integrity might be compromised if this is done, but that will depend on several factors.