Some images in the media can be trusted, because it's not like everything can be manipulated as an advantage. Some things don't even need to be manipulated for that matter. Although I do believe that most images in media are manipulated and cannot be trusted due to the misrepresentation of it. Obviously no one wants to make it known that their products are digitally manipulated but it's very misleading.
Fortunately fellow designers/ photographers can usually tell the difference between a photo that's manipulated and one that's not. It's not always that obvious but when you fathom the possibilities of photo manipulation it's hard not to be able at least a dozen things has been manipulated.
I can't be hypocritical and say that not informing your audience of manipulation is not okay because I do it a lot. But depending on the nature of the media and the cause for manipulation... Some may deserve an explanation or at least a notice that something has been manipulated. It should probably okay in most cases since manipulation is probably the number one factor of good advertising. Sometimes it's not always bad but always letting people know when something is manipulated wouldn't hurt because it won't undermine our advertisers trust but at the same time it gets us where we need to be, to be successful.
