Optimize your image sizes to generate great previews when posting a link on facebook

Sharing your website posts on facebook can drive more traffic. You should therefore optimise your photos that will appear on your share post.
So here is our tip:
Use images that are at least 1200x630px for the best display on high resolution devices. You should use images that are 600x315px at the minimum to display link page posts with larger images.
If your image is smaller than 600x315px, it will still display in the link page post, but the size will be much smaller.
You should also have an aspect ratio as close to 1.91:1 as possible to display the full image in News Feed without any cropping.

source:
https://www.facebook.com/PagesSizesDimensions
http://goo.gl/oCUkyd

Facebook timeline Images Best Practices

One of your most frequent questions is about the optimum dimensions of an image in timeline.
Well, when you post an image you have to think that there are two primary locations that your image will appear.

1. In your timeline where the minimum for displaying right is 504x504px (http://goo.gl/3bf6kI).
2. In your fan’s newsfeed, where it should be at least 472x394px ( http://goo.gl/19XH99 ).

Our recommendation is:

Use 4:3 ratio or more landscape images with a minimum 504px width.
You should also try to stick in one the following widths if you want to avoid compression:

• 720 px
• 960 px
• 2048 px 

Keep in mind that a photo should be less than 100 KB to avoid compression and cannot be more than 25 MB.
Save your image as a JPEG with an sRGB color profile.

Why to do so:
4:3 is close to the 472:394 ratio and is more common.
On the other hand 504px minimum width will keep you covered for the blanks on the sides.
Finally from Facebook we get the following:

Resize your photo before you post it.
These are the sizes (width) we support:
Regular photos    720 px, 960 px, 2048 px
If you use a 2048 px photo, make sure to select the High Quality option when you upload it.
Save your image as a JPEG with an sRGB color profile.

Some extra info:
In addition to the page timeline and the fan’s newsfeed, photos will also appear in the photo stream. Finally let’s not forget that Facebook also allows photos to be posted in comments.
In all of these locations, if a photo is clicked, the photo will open in full-screen mode.

source:
https://www.facebook.com/PagesSizesDimensions
https://www.facebook.com/help/www/266520536764594