Wouldn't it be nice to post a picture or image on your Facebook timeline and have it fit perfectly without forcing readers to enlarge the image to see it all? You can void having to enlarge the image on your timeline by creating at a certain dimension.

Resize your image to 403x367 pixels, that's 403 pixels wide and 367 pixels tall.

Facebook timeline image size example:

Create images using this dimensions and the reader won't have to expand the post to view it all.