I think from an etiquette point of view, it can be important to indicate that you've taken something out of its context (which of course, you should never do w/ the *deliberate* attempt to distort its meaning).
and the *how* of how you do that is something that (I believe) isn't particularly crucial.
Some people put "<snip>"; others put ellipses; others simply quote a single graph out of a larger block in the assumption that people will realize that the surrounding graphs were removed; others quote the whole graph but bold the one line they want to focus on (I like this bcs it keeps the context, which is often important).
Basically--be clear, and don't misrepresent someone's views by what you left out (and don't leave stuff out sneakily).
I don't know if other people are like me, but I can interpret all those methods (and some others not mentioned here) quite readily.