What is the maximum pixel width an image in a post can have, to be displayed without getting resized on the desktop version?
All images posted on SE are subject to the post's maximum width, which is 660px.
A single 660x100 image
Two 330x100 images without space/linebreak
Over 660px, then the image will get resized automatically to fit the post's width.
A single 800x100 image