Timon,
Welcome!
We need to know a few things,
1. what camera are you using?
2. What are the settings for the camera, F-stop,ISO, shutter speed and is it on a tripod?
3. What lighting are you using?
It looks like the lighting is pretty good,can't tell about the color. You need to use a relatively good camera, a DSLR would be great. You also need to make sure that the front of the lens, is perfectly parallel to the art work! If the artwork is on an angle, the camera needs to be on that very same angle. If not, part of the image will be sharp and half will be "soft" of slightly out of focus.
The camera HAS to be on a tripod or a solid surface, you can't hold it right and get a good copy. Ideally, you should use the smallest aperture, F8,F11,if you have a DSLR type camera. The "focal" length should be longish, like 75 to 100 or so. If you use the wide angle lens, it will distort the image,since you'll need to be too close, so a longer lens is much better.
Here's my tutorial on copying art work the right way:
http://fineartamerica.com/showmessages.php?messageid=2359806
Good Luck,
Rich