Feel free to use them. I won’t however be putting up different sizes. If you need a larger or smaller version there are many wonderful Image Editors that will resize beautifully. I myself use Irfanview. It rocks.
Just click the picture and it will take you to the Picasa Web Album. Decide which one you want and then click the DOWNLOAD button at the top and when the window pops up click SAVE. Decide where you want to save it. And then do as it says.