It seems like it should be a simple task to copy a photograph, or painting and with experience it is. In a controlled environment it starts with squaring the camera to the artwork. The easiest way I know is to place the art on the floor, or low table surface and level the camera above it. Two lights should be placed at 45 degree angles to the right and left and aimed toward the center of the art. I use two umbrellas to bounce the light. Depending on the room you are in, be careful of color casts caused by wall colors. Depending on your light source, set your camera to the appropriate color temperature. After making the exposure, I bring the image up on my monitor to review the color. The original is placed under the light it was photographed with and compared to the screen image. This assumes that your monitor is calibrated. When shooting with flash I use a daylight bulb to light the original for review. With tricky subjects such as textured oil paintings, a linear polarizer may be needed to remove glare from the surface variations. If you do not have lighting equipment available, outside under a clear sky in shadow is the next best option. The only thing you will have to correct for is a cool color cast from being in shadow. You can do that with a filter, or in post production. As for lens selection, 50mm or longer is your best option and macro will give good results if you need to be close. If the work is under glass you may need to set the camera behind a dark panel, or paper with a hole cut for the camera lens to shoot through. The diagram below was taken from my blog, “Printer Under Glass.” Just envision your framed art in place of the printer.