Testing WIA without having a scanner/camera device

Not sure, but maybe http://scanworkssoftware.com/twainimporter.aspx will help you

or, Go to http://twain.org and under the "Fast Find" section click the last link titled "Sample Data Source & Application". This will install TWAIN 2.0 and a sample source named "TWAIN2 FreeImage Software Scanner" which has some basic scanning features. It does not have a driver interface but will let you preform scans and Get/Set some general properties.

This does definitely what you want: https://github.com/twain/wia-on-twain

I simulates a scanner and publishes a TWAIN and a WIA interface. Also the scanning of a graphical page is simulated, so you can try out different resolutions and colour schemes.