Mask + Image without black on destination

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Hi, essentially I have a mask and I make a bitwise_and between the mask and an image. This works wonderfully, but I cannot find a way to ignore the black on the destination image. Here's the process for more clarification :

http://img.photobucket.com/albums/v220/jaeko/mask.png

Essentially, I do something like this:

//Should dst have an alpha channel to replace black by a zero-opacity pixel?
cv::bitwise_and(image, mask, dst, mask???);