This is a fun little activity to do with kids (or if you just like to color yourself)! Start by taking a photo, or letting your little one take a photo. It can be of anything, a person, a place, or a thing. A few suggestions are photos of favorite toys or of family members.
Open up the photo in Photoshop or other photo editing software. The following steps are for Photoshop users, but similar steps can be taken in other programs.
Convert your photo to black and white.
Adjust your levels and contrast settings to make your image pop a bit more than usual. This will help when you add your filter on. Next, go up to the filter menu, and choose artisitc, and poster edges. For the example below, I adjusted the edge thickness to 4, edge intensity to 2, and posterization to 5. Play with the settings until you get your desired effect, or you can go with my suggested settings. (Tip- If you plan on making a lot of these, you can create an action so that each time you open up a photo you want to turn into a coloring page, you just run it through the action and it will automatically complete all of the steps for you.)
Once your filter is on, adjust your levels again until you bump the contrast of the image up so that there's primarily white, black outlines, and a small amount of grey shading on the darker areas of the image.
From here, you can cut out the background if needed (for an individual object, or copy and paste multiple objects onto one page if desired). You may also wish to clean up any edges with the eraser tool, and do a bit of dodging and burning. These are optional steps and may or may not be needed depending on your image.
Now you're ready resize (to whatever size you want to print it as), print, and color!
A few additional tips- The best images to use for this are images with a lot of light colors or tones in it. It's much easier to take a light color all the way to white then it is if you have one with lots of dark colors. Pre-visualize how your original image will translate into a coloring book page. Objects tend to work better then landscapes.
To turn this activity into a more educational experience, add text to the bottom of your coloring pages before printing with the name of the objects. For example, if you're trying to teach a child the name of their toys, and are taking images of those for your coloring pages, label each one under the object- "horse", "ball", "doll", etc.