Notice anything strange about this photo of Didier Drogba's return to Chelsea?

Chelsea and African football legend, Didier Drogba, took to his Instagram page to share a photo of himself and his former teammates at Chelsea's Stamford Bridge on Sunday 22nd of january. Included in the photo is Cesc Fabregas, Diego Costa, Willian and John Terry, but something about the photo has got people talking.. Do you know what it is?