To give a quick answer...
Keep art flat to plane of camera lens. If you tilt the painting forward ot backward any, and the camera does not match the tilt/lean, your square/rectangular painting will look wider on top or bottom -- it will be skewed and distorted slightly.
My concern about art outdoors is wind. It's so easy to damage a painting from simply hitting the ground. And then directy sunlight isn't really the kind of light you want. Even bright hazy daylight casts ugly colors and glare on objects. Put it in a somewhat shaded environment, but still getting adequate light for ISO 200 or less.
Re-shooting may actually be a bit faster than scanning slides. It is for me, at least -- even with my fast Epson V300 scanner.
To upload full-sized images, ZIP or RAR the JPEG image. Put the image in a RAR or ZIP archive file, then upload that file. It must be 8MB or less.
Some diections are here:
http://www.digitalfaq.com/forum/show...ages-1529.html