I think for ultimate quality, if its desired, images should be edited in your favourite image editing tool (Gimp) then uploaded.
If you have an image say 1000 px wide but your max content width is 600 px, you resize it with SS $Image.SetWidth(600) you're going to have quality issues even if your quality is set to 100
If you had a 2px border around the original 1000 wide image thats going to translate to 1.6px in the 600 wide image. This can't accurately render onto pixels so it gets blurred which is normal behaviour.
The blurring that occurs isn't so important for jpegs of people or scenery, as these images are already blurry and it's not as noticeable when the quality drops on resize. However in the example of SetRatioSize1200430-Legal-Situation-de.jpg it's Plain text on a white background. In these cases the quality drop will be most apparent. As you can now see, by the naked eye, the subtle blurring around the crisp outline of the text.
My rule of thumb, if its an image of text, logo, or flat colour like an icon. Use PNG format and don't dynamically resize. Export them at the right size and use them as is on the site. For images basically of anything taken by a normal camera, use jpeg and resize the hell out of em. Clients notoriously upload 3000px wide images straight from their camera and wonder why their site is slow.