But these are not online systems per se. For example, Squoosh is a browser extension. The conversion is done on the client side. Hence I say, that it makes more sense for the user to use their favorite tools to adjust the image, instead of using a system implemented by me.

As LoyceV commented, the most efficient systems that exist are native to PHP, which is GD or ImageMagick. They do their job well, but for those who like to see images always with quality - like me, I'm always a little reluctant to use these tools. Not to mention, that security is more exposed.

But I'm going to study the possibility of having an additional platform that performs these conversions and then sends the image to TalkImg.