Idol Worshipping is one thing and using idols to remind you of beloved is a different thing. Idol worshipping is not advisable in sikhism because idols can take you nowhere. Also Sikhs do no worship trees,animals, insects etc. They are no better than human so why should we worship them, we should worship what is better than humans at least. Simple. The photos(i know they are not real but an artist's impression), gurudwaras, shastras, Idols can help us to remind about them but they are not worth wroshipping. If they are used only for the purpose of remembrance, then I think there is no harm. But if one start worshiping (matha tex, washing with milk, putting flowers on top, dhoof batti, bells - shankhs etc.) them and take idol as a God, that's not beneficial.