Smush.It is a free image optimization service. Unlike other software, it is completely web based, and you do not need to download or install anything.
Most of the image optimization software, like RIOT and VSO, slightly impact the quality of images while reducing their size. However, Smush.It does a “lossless” optimization of the images. This means that image size is reduced without impacting image quality.
Smush.It is also different in the aspect that it uses image optimiation techniques specific to the image format that you provide. Using those, it removes the unnecessary bytes from images and reduces its size.
To reduce size of images, just path the URL of images in Smush.It box. Smush.It will automatically optimize that image, and will let you download the optimized image. It also shows the percentage and size reduction that it was able to achieve while optimizing image.
I tried Smush.It with a .png image, and a .bmp image. It was able to reduce the size of png by 20%. But for bmp, it was able to reduce the size by 57%! The best part is that I did not have to do anything – I just provided URL of the images and Smush.It took care of everything on its own. Pretty amazing.
You can specify URL of multiple images in Smush.It, and even provide URL of whole webpage. In latter case, Smush.It analyzes all the images in the web page, optimizes each one of them as per their native format, and then gives a zip file to download all the images together. Love it!
Here are two limitations that I found with Smush.It: It works on images up to 1 MB in size, and the images have to first uploaded somewhere. Both these limitations are quite small, considering the usefulness of this free image optimization software, and the fact that it is totally free.
You can try Smush.It here.