The first case is the same as “we have your picture” which does not necessarily mean that you are in the picture. In the second case, you are in the picture.
Good, better, best.
Bad, worse, worst.
Generally, no; sometimes, yes. Someone else might be able to give a better answer but, for me, it is idiom at we need to get used to with experience.
Hi Red,
You can not say “Most the speakers are of Germans”, and also this one “most the speakers are from Germans”, you should say “most of the speakers are from Germany.”
If you want to use “of” in your sentence, you should say “most of the speakers of Germany are talent.(for example)” and if you want to use “from” you should change the “Germans” to “Germany” because “from” here refers to a place not the people of that place.