Google is getting concerned about page load times. One of the factors that strongly effects page load times is the number and size images on a page. A few images, each image large in size, OR a lot of smallish images, each modest in size, will have an negative impact on your page load time, i.e. ensure that you page takes long to load.
If you would like to compress the images you use on your website, there is an excellent free to use compression tool from Yahoo developers named Smush.it.
I’ve written a step by step guide on how you can compress and then download your images for upload to your website. Do take a look