Thank you for contacting us.
For your issue, may I ask if you use the same webcam for the two situation.
Normally, white space indicates the ratios of length and width of image you acquired doesn't match that of our control.
If you are using webcams of the same type, you can adjust the length and width of our control to fit the image.
If not, it is suggested to set DynamicDotNetTwain.FitWindowType Property to make the image fit the window size. Please refer to:http://www.dynamsoft.com/help/TWAIN/.Net-TWAIN-Scanner/html/P_Dynamsoft_DotNet_TWAIN_DynamicDotNetTwain_FitWindowType.htm
If you have any further question, please feel free to let me know.