The word conversely is an adverb that means "the opposite" or "on the other hand." It is often used to introduce an idea that is different from one stated before. You say the photo is a fake. Conversely, the photographer claims it's real.
The adverb conversely has its origin in the Latin word convertere, which means "to turn about." In the following quote by Journalist Andy Rooney note how the word balances the two sentences: "The closing of a door can bring blessed privacy and comfort - the opening, terror. Conversely, the closing of a door can be a sad and final thing - the opening a wonderfully joyous moment."