There are a number of ways to digitize documents and photographs. The two primary ways are to use some form of a scanner or in the alternative, some kind of digital camera. Following is a number of digital files of the same document acquired for the computer with different options. In each case the document was scanned or photographed at the optimal level for the device. The file was saved as a .tif file and the image was magnified to 200% of the original. The images are screen shots of the magnified original signatures.
Flatbed Scanner: The first scan was done with a ConoScan 8800F Flatbed Scanner which is advertised at 4800 x 9600dpi. The image is supposed to be 400 dpi from the scanner. The file size was 17.9 MB.
High Speed Sheet Fed Scanner: The scan was done at 400 dpi on a Canon DR-4010C Scanner. The file size was 31.6 MB.
Newer Compact Digital Camera 12 Megapixels: This was done with a Canon A1100 IS. The file size was 3.2 MB.
Digital SLR Camera 15 Megapixels: This was done with a Canon 50D. The file size was 20.4 MB.
As you can see, all of the images are very readable and clear. The color change is a result of the lighting and can be corrected in Photoshop if needs be. Which one you pick really depends on the ultimate use of the image. If the image is being copied for content, then any one of the four are sufficient. However, if the copy is going to be used a substitute for the original for archive purposes, the flat bed scanner or the sheet fed scanner would be better images than the digital cameras. All of the images begin to pixelate at about 400% of normal size.
The purpose of this exercise was to graphically illustrate the ability to use digital cameras for archiving documents over the more traditional scanning methods. In case you think that the color cast on the camera images is objectionable, here is a gray scale version of the Digital SLR image:
For most purposes, digital cameras, even less expensive ones, are perfectly adequate to produce copies to be used as source material.