Photoshop :: Image Fading To Transparency

I need to make an image fade to transparency for a little projet of mine.

I tried to add a mask to my layer with a gradient [blanc to white] in it, in photoshop it gave the result I wanted, but when I save it as a PNG, the transparency is just not working like in photoshop. (Assuming I use it as an image in a website)

I tried to remove the contour thing, and photoshop see's only two colors [000000 and transparency] so when I open it in a browser, there is simply nothing. If I add a white background for exemple, the image will work, but I need the image to be really transparent so it can merge with my web background.