How Much Can You Quote / Share Before it is Too Much?

This is a question for the people who know, because I haven't found a clear explaination of this on any Steemit post yet. They are all somewhat vague as to what is or is not acceptable.

I know that I can use my own images and stock photos that I have purchased online, but what about images from articles that I am referencing?

So in a recent post of mine, I used a Steemit image, a Problogger image and an image from LifeHacker.

• Steemit image: I assumed this was ok, because it was promoting the platform.
• Problogger image: It had the logo clearly on it, so I think that is fine - isn't it?
• LifeHacker image: I referenced the article in the text, so I think its ok to use the image right?

Also, how much of text are we allowed to use in quotations? I think I remember from school it was like up to a paragraph or something, does anyone know?

Also what about sharing videos?

My thought process about it is that we are providing free (to them) advertising for their content which drives more viewers and subscribers to their channels (which pay aka YouTube). So is this acceptable?

If I missed a post which accurately describes this, please send me the link or share it here because I am sure many people, including myself, will find it useful.