Some people have noticed that on my blog, I have images that are small, but when you click on them, they popup to show the image in more detail.
Say you have this adorable picture of a puppy, but you want people to be able to click on it so they can see how truly adorable the puppy really is. (Go ahead, give it a click. You know you want to.)
To accomplish this, when you insert your image, choose Link to: Media File and for Size, choose Full Size. Then, if you are using the visual editor, drag the corners of the inserted image to make the image the size you want it to be in your post. If you are using the Text editor, you can adjust the image where it says width=”800px” and either remove the height or change it to “auto”, like this:
One other note, WordPress default behavior is to open image in a new window. If you prefer the popup like I have on this site, just grab the Easy FancyBox plugin.