In my job as a Web Application developer, occasionally designers send me images to place on web sites, which is usually fairly simple. However sometimes I receive images from print-orientated designers, who use Adobe Photoshop to create images in CMYK format. These images are great for printing, however they don’t work too well on the web (most browsers won’t even render CMYK formatted colours), so it it’s usually best to convert them.
The GIMP can’t load CMYK images (yet anyway) , and although Krita can open the images fine, changing the colour type usually results in the colours in the image changing. The only way I’ve found to convert the images on Linux is using ImageMagick.