How can I view all my images as thumbnails without folders?

I want to clean out my photos so I can start organizing them on my Macbook Pro Retina, but I can't figure out how to just view all of the original image files as thumbnails. They're all split up into confusing and some seemingly identical folders. Is there a way for me to just view all of my original image files at one place in finder so I can effectively clean them out?