Hash values of files sent via MMS can vary
Multimedia Messaging Service is used by cell phones to send video, audio and multiple images. It contrasts with Short Message Service that can only send text up to 160 characters in a message. Unlike other files collected from a mobile device, images sent on separate occasions via MMS can have different hash values. A study conducted by researchers at Purdue University concluded that, " While the results for the majority of tests were uniform, the hash values reported for data objects transferred via Multimedia Messaging Service (MMS) were variable." Shira Danker, Rick Ayers, and Richard P. Mislan, Hashing Techniques for Mobile Device Forensics, 3 Small Scale Digital Device Forensics J. No. 1 (June 2009).
The study shows that the same JPEG file sent via MMS on different devices at different times would have an entirely different hash value.