Custom mask
Make certain parts of your dialog's window transparent. You can use this option to make a custom window shape for your dialog.
To specify the areas that you want to make transparent, you need to create a transparency mask file in your favorite drawing program.
A transparency mask file is just an image where a single color represents the parts that you want to make transparent. Picture this image as being invisibly "placed over" your dialog's window, like a mask or a stencil.
In AutoPlay, the transparent parts of the mask should all be solid black. Wherever solid black appears in the mask image, the corresponding part of the window will be made transparent. The transparency mask acts like a "cookie cutter," cutting holes in the dialog's window so the user's desktop can show through.
Click the Browse button to select an image file.
Note: When some of these options are used, the controls that normally appear on the title bar-such as the "X"-shaped close button in the upper right corner-will not be available. Make sure you provide some other way for your users to exit from the dialog. (For example, you could have an "Exit" button somewhere on the dialog.) You can also exit the dialog using the Escape key, or ALT+F4.