Cameras with higher resolutions will produce higher quality scans. Digital camera resolution is normally measured by the total number of pixels it can capture (e.g. 10 MP, or 10,000,000 pixels). Scanned documents, however, are measured in dots per inch (or pixels per inch). The resolution of your scans is determined both by the camera resolution and the size of the media that you are capturing.

Acceptable resolutions range from 200 dpi to 600 dpi, depending upon the image source and the desired level of compression. http://www.loc.gov/preserv/guide/guid_exp.html This assumes that the document is not zoomed or enlarged.

Max Theoretical Resolution

For a typical camera that has a 4:3 screen ratio, the equation for max dpi is:

X=√(4/3*1000000*MP)

Y=√(3/4*1000000*MP)

So for a 12 MP camera, the maximum theoretical resolution is 4000x3000. To then determine the max theoretical resolution as dots per inch, divide the smaller number by the length of the shortest side of the media. In this case, if the media was a US Letter sheet (8.5 by 11 inches), the maximum theoretical resolution of the scan would be 353 dpi.

Actual Resolution

'''The actual resolution of your image will always be lower than the theoretical maximum resolution.''' There are two reasons for this. First, the internal components of the camera prevent it from actually capturing the full number of pixels. http://electronics.howstuffworks.com/cameras-photography/digital/digital-camera3.htm Second, your media probably isn't in a 4:3 ratio, so it will never perfectly fill the entire capture area.

To determine the actual resolution of your image, simply take an establishing shot with a ruler on top of the document, and then use image editing software (e.g. GIMP) to measure the number of pixels contained in an inch on the ruler.