Photobombing is an unpredictable and very often spur-of-the-moment activity.
Sometimes, you just have to seize the moment and dash across a red carpet/tourist attraction/motorway at full pelt in order to jump up and down while gurning at the back of someone's holiday snap. And other times, it's just handed to you on a plate...
Take Jack Black, for example. He's clearly had to put in no effort whatsoever in order to photobomb co-star Zac Efron at this press conference for Dr Seuss' The Lorax.
All the same, he proudly posted the picture on his Facebook page, along with the caption: "Yes, Zac Efron - I will photobomb you any chance I get!" (Watch out, Zac!)
Of course, it's not the first time a celebrity has indulged in the 'sport'. Take a look at our brilliant gallery below - and yes, it includes a previous Jack Black classic...