Adding images to pages

I can add an image to a page, but it seems limited in it’s size. For example if I upload a 10×20 image, it shows only about 10×10 of the middle of the image. Can I remedy that?

Also, is there a way to show a thumbnail on the page, and make it clickable so it opens as a large image?

I hope I’m making sense and someone can help me out!

Thanks…