Will you get into trouble or sued if you use pictures that are not yours on blogs?

Let’s say you want to make a blog…. Can someone sue you if you use a picture that is not your own? For example if you have a “Movie Review” type blog, and you use Google images of that particular movie on your blog post… Can you get in trouble for that? Is that copyright infringement? Is it ok if I leave a reference at the bottom of the post linking the photo to where I found it? Help!

Or let’s say I do a blog about flowers and I use a picture of roses(not my own) that I pulled up from Google search or Yahoo search…. is that copyright infringement? Can I get sued?