why do my boyfriend get mad at me when i post his picture on my instagram?

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well sometimes he sends a video playing piano for me,and i also found some pictures of him that are really cute,and those things mean a lot to me,then i posted some of them on my instagram,i cropped most of the pictures and videos so people cant see his face,eventho he is really charming,but then,he became mad at me,i am wondering why,because those pictures doesnt have his face on,hes like,avoiding from people to know that we are in a relationship,im dissapointed,can someone tell me what actually is going on?
not exactly,he said,people will still know that that was him and it is quite humiliating