First of all, "DLL" is pretty much insignificant to .NET, this is no more than the file naming convention. Essentially, anything which can be used as a library is
assembly
.
You can use either
System.Drawing
or WPF, but not both together. More exactly: even though there is an interop library to use them together, it would be quite artificial for new development; it is designed for interoperation with some legacy code.
The topic is pretty wide, it could take writing some article per library to cover the topic, so you can start with this:
http://www.codeproject.com/search.aspx?doctypeid=1&q=%28%22Web+camera%22+OR++Webcam%29+%22C%23%22[
^].
After you find some basic information, select the library to use and make the first simple working prototype application (it could be done in matter of few hours or just within one hour), you can ask more questions if you face any problems.
—SA