I have found this picture of Manuel in a new biography published in Portugal last December ("D. Manuel II, O ┌ltimo Rei de Portugal by Ricardo Mateos Sainz De Medrano). There are several pages filled with extraordinary rare pictures such as this, but unfortunately I wasn't able to buy the book yet. According to the author, this picture was taken at Grand Duke George Alexandrovich's villa in Likani when Manuel was visiting him and his mother, Maria Feodorovna. I took this picture with my phone, so the quality is not the best, but I just couldn't resist. I think this is the best picture I have ever seen of him:
Have had a glance on it, but haven't decided whether to buy it.
Apart from lots of photos, many of them I had never seen (like the one you posted) there seems to be hardly anything new...
Maybe I will give it a second look