There is no problem in putting a picture on the article, but do you have:

1- A picture which clearly represents Muhammad in accordance to the textual descriptions of his physical appearance as well as his life?........and IF there is such picture available then:
2- Is that Picture Credible and cited in any scholastic works Notably?
3- If above two conditions are met AND the picture NOT titled as "Muhammad." but by the artists reference 

If above three conditions are true then I am right here to support the picture. Otherwise please find out such picture and come back.