First, decide between using a camera to capture your work or a scanner.
For me, that was an easy choice. I come from a photography background, so I already had the knowledge and camera required for good photos. But even more importantly, I often paint very large - sometimes up to 4 feet paintings, and those cannot be scanned!
If you want to scan your artwork, but you don't own a large scanner, you'll need to find a local print shop who can scan large artwork, and they have limits (and it can be pricey).
So this information is for anyone interested in photographing your artwork. This is MY process, and it may differ from other artists, but I hope it helps! Everything in my portfolio was a photo taken with my DSLR and cropped/adjusted in Photoshop after.
Anytime I say "canvas" I am referring to your artwork, whether it's a painting, drawing, or sculpture!
There are lots of factors to consider when documenting artwork, but lighting is the main challenge. Regardless of your equipment, if you don't understand what good lighting is, your photos will suffer.
USE NATURAL LIGHT WHENEVER POSSIBLE (But not direct sun)
Each type of light (natural, incandescent, LED, fluorescent, etc) has a different color or "temperature" (warm vs. cool)
Natural light falls in the middle, giving you a very neutral color and most accurately representing your artwork's colors.
Most of us have incandescent or warm LED bulbs in our home, which will cast a warm glow. If you absolutely cannot take photos using natural light, using the artificial light available to you is OK because color can be fixed in post production (to an extent). However what is not OK is low light, or using flashes that create a glare on the artwork. Sometimes, the glare isn't just a white reflection, but a color shift within your shadows. This can be hard to notice until you get into post production, and it's really annoying to fix!
To avoid reflections and glare on your canvas, you need to use indirect lighting. This means making sure there are no direct sources of light hitting your canvas. You can do this by angling your canvas in a certain position with your room. Fill the room with as much light as possible. Don't point light directly at your canvas. Begin angling the canvas and really look at the shadows. If you notice they are "lighter" than they should be or have a slightly different color, this means there's a glare and it WILL show up in your photos.
Keep angling until you find a position that works! Remember to avoid casting a shadow on the work from your body, camera or tripod (I rarely use a tripod).
The angle of the photo matters!
Don't take the photo from a harsh angle (from the side). Position the camera DIRECTLY ABOVE the canvas, keeping in mind that you will need to crop the image. Cropping requires straight lines.
The following examples were taken with my phone (LG G4):