How didn't Jafar recognise Aladdins face when he disguised himself as Prince Ali?

Jafar didn't know it was Aladdin until after he attempted to have him drowned. When he saw the lamp sticking out of his hat in Jasmine's room. Prior to that, I think there was a jealousy or need for Ali out of the way because he had just begun his plot to make Jasmine marry him.

To answer the question, tho someone did above, you'd be amazed what a bath, fresh/rich clothes, posture and other things can do to change one's appearance. It's like Superman.

He may have felt Aladdin seemed familiar or something was off about him but he did not recognize him and hid it to trick Aladdin. He had absolutely no idea who Aladdin was until after the stunt in Jasmine's room. the next scene after escaping the guards is him cracking up in the dungeon and yelling at Iago that Prince Ali is that 'street urchin, Aladdin'. If he had known from the beginning, he would have been plotting for a way to get the lamp from him from the very beginning (and he would have known Aladdin had the lamp considering he knew Aladdin was poor and would not have had that kind of transformation so quick).