Hello! I was like you a while ago. I was using - http://www.imgopt.com/ but still I was noticing that the images are not loading as fast as I wanted. Moreover, I always get some suggestions in the speed evaluation sites about the size of the pictures. So, I searched online and found a great site!
Here it is my friend - https://compressnow.com/
This site is the best one for compressing and reducing the size of the images! Flawless! :-)))))) There was an image 45Kb and after the compression it was 18Kb!!!! Amazing!
I was using https://compressnow.com/ before...
It has some problems with .png format! It simply downloads all the images in JPG! And transparency is needed sometimes ;-)
I am using the suggestions in https://gtmetrix.com - simply run your site and click on "Optimize images" - after that you will be able to download the optimized version of your original image!
I am using these: