Verify alternation and tracing the source of digital photos

Hi List,

A case of digital photos circulated on the Internet formus, I need your 
helps in find out answers for 2 answers:

1.    Are there any tools that we could used to verify if a digital photo 
has been altered?

2.    As those photos are posted on various formus, how to trace back the 
original source of the photos?  I think even though we could obtain all logs 
(for timeline analysis) from the forums that those pictures are found, but 
we could not rule out that some more sources are missed.

Thanks for answering in advance.


Frankie 


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