Do anyone have an idea about the exact etymology of this word? Also, would it be correct to use the same word when referring to a live broadcasting on television? Or would the term videobomb be more appropriate?
On May 6th, 2008, the earliest known Urban Dictionary definition of photobombing was submitted by user U8IK, which was later highlighted as the Urban Word of the Day (on June 20th, 2008). Within days, groups dedicated to photobombing formed on the Internet. By August 21, 2008 it was in in common use.
Russian gymnast Anna Pavlova, who recorded an imperfect 0.00 for one of her vault attempts, could try to land a photobomb of herself mugging in the background of all those photos that will be taken of Phelps lugging around his gold. - Daily Herald
Oxford Online proposes that it may have come from Google bomb: An attempt to make a search term return a website for an unexpected person or organization when entered in a search engine (typically for satirical or humorous purposes) by the creation of numerous links to that website from pages including the search term.
A related term is videobombing, which applies the concept to video footage instead of a still photograph.