Radical Image Optimization Tool (RIOT) is a free program that lets you compress images in your computer losing little to no quality. Here is how you can download and use this free program.
Step 1- Download the software
The first thing you have to do is download the software. To download the software, go to the following website: http://luci.criosweb.ro/riot/ 
Next, click on the download link, and download the software to your computer. The download process should take the no more than a minute, because the file size is only about 1 MB.
Step 2- Set up the RIOT
Once the download process is completed, extract or unzip the downloaded file. This can be done with winrar or 7zip. Next, click on the setup file and start the installation process.
Step 3- Start compressing images
Once the installation process is complete, you are now ready to start compressing your images. To compress your images, open the program and drag an image file into the window. Compressing images in this program is very easy and effective.
After you drag an image, RIOT will then display two screens: a screen of the original image on the left, and a screen of the compressed image on the right. RIOT will then give the option to compress the image. It is recommended to select a quality of 75 percent, because you will barely notice any change picture quality.
Do you how the file size nearly decreased by half when the quality is decreased to 75 percent? The file size decreases a lot of decrease the quality further.
The picture that was shown has a resolution of 3072 by 2038 pixels–which is a lot. Notice how you not could barely make a difference in quality between the optimized and initial image. This program was tested further by decreasing the quality by 30 percent. The file size decreased to only 200 kilobytes, and the picture still looked crystal clear.
This is a great tool, it is strongly recommended to download it.