To save an image with a transparent background:
1. Using the Magic Wand Tool, select the color you want to make transparent.
2. Choose Help > Export Transparent Image…
3. In the first screen of the Export Transparent Image Wizard, choose one of the following, then click Next.
a. If you chose a transparent background when you made the new image, choose the first option.
b. If you have already used the marquee tool to select the area to be transparent, select the second option.
c. If you haven’t selected the area to be made transparent, choose the third option.
4. In the next window, to use the image for the web, choose Online, then click Next.
5. In the next window, choose GIF for the format. PNGs are not widely accepted as a format, so a GIF is really what you want.