I heard a rabbi giving hadracha to his Talmidim. He told them [among other things] that if they see a Gadol BiTorah at a simcha or the like, they should approach him and ask him questions!!
I see where he is coming from but would like to present an alternative opinion.
Gedolim are people too!!! Maybe they don't enjoy being "hocked" all day and all night seven days a week with questions. Maybe they need to relax from time to time.
So if you see a Gadol standing alone at a simcha, approach him, smile, say Shalom Aleichim and quietly walk away. If you have a compliment to say - say it. Big rabbonim enjoy compliments b/c they are human. "I listen to the Rav's/Rosh Yeshiva's shiurim. I love them. I thank the Rav/RY very much." "I learn the Rav's/RY's sfarim. They are amazing!!!" Then walk away.
Better - hand him a check for his shul or Yeshiva!!! THEN walk away.
IN OTHER WORDS - instead of thinking what you can GET from him, think of what you can GIVE him!!!!!
WOW!!! A revolution in thought! Other people are not just here to meet my needs, be they spiritual or material. They are here so that I can meet THEIR needs, be they spiritual or material.
Ahhhhhhhhhhh - but what about learning from him? Learn his sfarim, attend his shiurim etc. etc. But PLEASE - don't unnecessarily "hock" him [or ask for a picture!!] unless you have a compelling reason to do so.
What about asking for a Bracha? Maybe. But you can get a Bracha from an even BIGGER Rebbe. Hashem. If you keep His Torah, you will be blessed!!!
