Why would a person behave in such a way?
There is someone (of the same gender) who you know is kind of jealous of you and tries to compete with you. So if you upload a picture of yourself, they'll immediately upload a picture of their own self (not with the intention of "just sharing", but with the intention of trying to "compete".) You are sure of this intention since you know that person very well. What is the mental state of such a person? Is it some insecurity or is he/she trying to prove that he/she's better than you?