Do not take my ad hoc tests as a scientific proof. The results may vary from shot to shot. My tests only show that a digital camera can be as good (and much faster) for scanning as a cheap scanner.
For professional comparison of practical resolutions see
http://www.robgalbraith.com. The author provides tests for all the cameras reviewed. (The link didn't work for me today because of Gateway Timeout. Probably a temporary problem).
When deciding on which camera to buy remember about a remote capture feature, which is available for most Canon and very few other cameras. Check
http://www.breezesys.com/ to see what cameras the author's Psremote program supports. Also, make sure that the camera can be powered by an external AC power supply.
From
http://www.steves-digicams.com, I quote:
"RemoteCapture allows you to operate the camera while tethered to a computer via the USB port and includes a live viewfinder option. The Field angle/flash screen gives you access to settings for: Focusing Point, Flash, Macro Focus, AF-assist lamp and AF operation.
The Image Size and Quality is selected at the top. The shutter can be tripped by either a mouse click or a hot-key on the keyboard.
Captured images can be saved directly to the computer or they can be stored on the camera's CF card and then transferred to the hard drive
The Remote Capture program is also capable of interval and timer recording as well as instantaneous. Shooting interval: approx. 1 – 60 min. (1-min. increments) Number of shots: 2 – 100 shots (Maximum number of shots varies according to memory card capacity"
Avoid compact cameras that need a cradle to download images or to recharge batteries (unfortunately that is the feature of my Casios - two different cradles for two similar cameras). Camera+cradle+power supply is no longer compact.
If I were to buy a compact camera today, I would choose Canon Powershot A640 or a successor.