no resizing for one category only

Hi Guys,

I have a specific category called ‘slider’ to hold the posts that go into the featured slider on the homepage of https://www.corkstudentnews.com.

Obviously I do not want these thumbnails resized like the other categories’ ones, as because it’s quite a big sldier (580×200), you really notice any loss of resolution.

Does anybody know of a way to prevent auto-resizing upon featured image upload in just one category only? Or to assign a featured image directly from a URL?