PhotoShop is synonymous with image MANIPULATION.
There's a widely-written about case here in the States in which a police lab intentionally manipulated DNA evidence.
Any evidence can be manipulated. At least here, what makes something viable in court is the person who attests to the authenticity, not what tools were used.
Jeff Spirer
Photos: http://www.spirer.com
One People: http://www.onepeople.com/
Surfaces and Marks: http://www.withoutgrass.com
