Photos of drawings can be hard to get the lighting right (even) without a studio setup. I would scan them and clean them up in PS.

White trace is pretty easy to clean up. I use levels and take the right slider (white point) and push it left to remove most of the background stuff. Then use the middle (mid-tone) and left (black point) sliders to get the contrast dialed in. From there a bit of the clone tool will clean things up.

Cream and yellow can be dome this way too, it just takes longer.

That's just one way - there are quite a few.

Photos of drawings can be hard to get the lighting right (even) without a studio setup. I would scan them and clean them up in PS.

White trace is pretty easy to clean up. I use levels and take the right slider (white point) and push it left to remove most of the background stuff. Then use the middle (mid-tone) and left (black point) sliders to get the contrast dialed in. From there a bit of the clone tool will clean things up.

Cream and yellow can be done this way too, it just takes longer.

That's just one way - there are quite a few.

In the levels panel, click on the little eye dropper on the right (the white one) and click on your background. This sets that colour as 'white'. The same can be done for the mid-tones and black with the other droppers. This usually helps and can avoid blowing out an image by moving the white too much.

Scan it. You can keep more of the true details of a drawing through scanning. When you scan, scan it at least 180 dpi. And then in photo shop, there are two ways to make the trace lines disappear. The first is with the Levels (ctrl + l), OR which I prefer using, is Selective Color (Image>Adjustments>Selective color), what selective color does is it will change the specific color of that object to the colors provided (Cyan, red, yellow, black, white, blue). This is all assuming that you have Photoshop.

also try scanning it with a sheet of white paper behind it. As well try scanning it in a both color & b&w in case you need to overlay. It can save you some of the guess work.

good luck

control-l. Levels are your best friend. In addition to what threshold said, you can use the black and white eyedroppers to click on the image to set black and white benchmarks to get you into the right neighborhood. Even my dad can do it.

What jhooper said. My old bosses sketches were always on trace, yellow at that, and they always looked good in the end.

they'll come out fine. I'll bet they look better with a little crinkle in them, makes them look less perfect.

Always adjust the levels a little, it almost always helps a photo/rendering/drawing.