It means that the picture cannot actually show how great and wonderful the building is.

"Do it justice" in this context is an idiom which means, represent something in the way it deserves. So if the picture "doesn't do it justice" it doesn't show the Eiffel Tower as being as large, imposing and impressive as it actually is. You can use the idiom when talking about a representation or description of anything or anyone e.g. "How I've described her doesn't do her justice" (I haven't got the words to represent her as she really is).