The default resolution for images is 300 DPI. You can change the default resolution by opening the "Printers" folder, right clicking on the Win2PDF icon, and opening "Printing Preferences".
In the Printing Preferences window, click "Advanced...":
The resolution (Print Quality) setting us under the "Graphic" section of this window.
Set Printer Resolution
Available resolutions are:
Increasing the resolution will improve the quality of images, but it will also increase the document size.