Looks like you are not very clear on what a Webservice is? Have a read
here[
^] just to be more clear.(Just picked the first link of Google! If you want, pick any other.)
Using a webservice you can surely do the storing part of the image in database but not 'scanning'.
For using a Webservice, make one, expose it, then reference the same in your windows application such that you can talk to it. Once you have scanned image with you, use the webservice to store that. You will need to create an object of webservice and then uese one of the exposed Webmethods in it.