1. Create a grayscale Bitmap or JPEG file. Make all regions of the transparency mask white if you want that region to be 100% transparent. Black regions of the mask are completely opaque (0% transparent). The mask is then merged with the original image to produce a new image that is the product of blending the original image with the transparency mask. The Mask will be scaled automatically to fit the original image.
2. Feathered edges produce nicer looking blending between the mask and original image. A Gaussian Blur filter works very well to feather edges on a grayscale mask.
3. When you are finished creating the Bitmap or JPEG, copy the transparency mask to "Mask" directory.