Do you count using photo references for poses as plagiarism?

I'm going to ask a very blunt question here and I know not all of you are artists but I still want peoples opinions regardless, I had a debate with my teacher just today actually about what kind of reference could be allowed for a piece you'd actually be selling or product. What's considered acceptable? The reason I'm asking about this is because when I draw my artwork is dramatically better because I'm using reference for my pose with construction lines, I'd never use other artists' work for this and she wouldn't either but my teacher seemed convinced that under most circumstances using real life photo's is fine.

So what about you lot? I'm just in a never ending debate with this in my head and I've noticed the internet is as well, the problem is it really does improve my work a shit ton and makes my life a lot easier but I keep thinking just because it makes it easier it's cheating but apparently most artists use references for poses etc. like this unless they're doing abstract and so on.