SmushIt is a online tool that optimizes and compresses image losslessly without losing any graphics quality. SmushIt is a tool developed by Yahoo for web developers and designers to optimize the images so that websites can load much faster which provides better experience to the visitors. And it does really work as it compresses the size of the image which makes the browser download less to load it much faster.
SmushIt offers a easy graphics interface where you can upload multiple images with different format. You can also use image URL for compression.
You just have to select the images you want and let it upload and get compressed. You will see the compression data below showing the compression Result size(size of the compressed image), Savings(size difference from original image) and %Savings(percentage savings from the original image).
After the compression is done. You can download the compressed images to your PC in zip format from the Results tab.
If you are a WordPress blogger then you can try the WP-SmushIt plugin which optimizes images as you upload them to your site in background.