That is possible, but not specifically because the image is CMYK, but because the image is very large (2MB+). The Verify URL feature downloads the first 2MB of the media file. If the artwork is about 2MB or more, then your ID3 headers will exceed this 2MB, causing the verify to fail.
In general CMYK images (typically in png format) will be very large in size (1MB+) and the size increases based on the image size and number of colors found in the image (every slight shade color change is considered a separate color). The only time a CMYK is not large is when it uses only a handful of solid colors. CMYK images are optimal for printing, not screen viewing.
RGB images (typically saved in jpg) are optimal for screen viewing. The number of colors in an image do not impact the file size nearly as much as a CMYK image. A typical 1400×1400 jpg image will be about 200-400K, where-as the same iTunes image as a png will be 1-4MB in size. Note it is possible to save a png in RGB, but most editors default to saving png images in CMYK, thus we recommend saving your images in jpg to avoid this complication.
iTunes specifically will not display CMYK images.
Another important factor here is the ID3 headers need to be efficiently saved. If you are using a large image in your ID3 headers, it will directly impact the ability for your media to play promptly when streaming to a web based player. The first 2MB of the file need to be downloaded before the actual recording is found in the file. On high speed broadband connection this may not be an issue, but it comes into play when someone is using 3G/4G service that is not performing optimally. Prompt playback is critical, it is common for a listener to hit the back button in 2 or more seconds if the media doesn’t play.
My original response is also important, if your media is using a VBR, the verify feature will fail as well. This is because the only way to correctly obtain the length in seconds of a VBR recording is to read the entire file. As I mentioned before the verify feature only downloads 2MB.
