Facebook automatically optimizes images. We posted a 410k image on Facebook and then we downloaded the image. The original was almost 10 times the size of the Facebook-optimized version with little loss of resolution when viewed at 100%. Images for websites should always be optimized so they’ll load faster, but not everyone owns image editing software like Photoshop.

How to optimize images for the web without Photoshop:

First: Post the images to Facebook
Second: Download the photos from your Facebook post to your computer
Voilà—the images are now optimized for the web and can be uploaded to your website or blog.

Be sure to re-name the image, because it will now have a Facebook designation, like 11890922_464771667027316_n.jpg.
Search engines like names that mean something, like gardening-with-wheelbarrow.jpg