Why does he still send me a fake pic of him!!?

Right hear me out. I’ve known a guy online for a LONNNGGG time and in the past he used to lie. Anyways a couple years go by and we get into contact again. I’ve been seeing the way he is and hes not been lying at all till he sent me a pic today of himself, newsflash it’s not him it’s his BROTHER. How do I know this you ask? Well , I do background checks over guys and I pretty much know for a full fact that the picture he sent me is his older brother because I literally lurked through everything and I KNOW it’s not his real pic. That doesn’t matter though - do I admit I know it’s not him or just agree to be like “oh nice pic” I DONT WANNNA SAY UR BROTHERS HOT.