Recently while reading some website i came across an article about pictures of the Gurus that were painted during there own time and how we still have them. On Page 5 of the article there mentioned how in Baghdad Guru Nanak Ji Maharaj give permission to the king of Baghdad to paint Guru Sahibs Picture. In the article it mentions that a European named William Ouseley published a book in 1797 call "oriental Collections vol II". William Ouseley found this picture of Guru Sahib in a Baghdad palace and put the picture in his book. I searched for the book and found it, where it has Guru Ji's picture. There are two pages one gives a brief description and the second has the picture.
Here are the pages with the pictures