True if the Picture has an alpha channel.
A Picture that is created with the constructor that omits the Depth parameter has an alpha channel and old pictures can be converted to this format with the following code:
If input.HasAlphaChannel Then Return input
Dim result As New Picture(input.Width, input.Height)
result.Graphics.DrawPicture(input, 0, 0)
For pictures using masks, HasAlphaChannel returns False.