Compressing your images means faster page loading.
The idea is to optimize your web images so they load as fast as possible on your site.
Some people think that this doesn’t really apply to WordPress.com sites because the servers are so powerful that they can deliver anything fast.
You will discover that is not so if you upload a large background image and watch it creep down the page as it slowly loads.
What does big mean?
Big means anything over about 50KB. But crazy big means anything bigger than a few hundred Kilobytes (KB).
I know some people upload full-size jpegs that are several megabytes in size. This is one sure way to kill the speed of your site.
One of the things I like about the Ranking Easy optimizer is that it compresses images at different compressions and shows you the results on the screen.
You can see the artefacts in the high-compression images, and you can find the happy medium that will be just right for that particular image.
You can then download the one you like.
You can use the optimizer by inserting the absolute path to the image on your webpage.
Here is an example of an absolute path to an image.
Or you can upload an image from your computer into the image optimiser.
Here’s the link to the Ranking Easy Online Image Optimizer.
Doesn’t Picasa Creative Kit do this?
You might want to catch up on the latest news about this in the update I added today to an article I wrote about Picassa in 2012. I added a comment about why I would never upload a full-size image to any online image editor.