When saving assets for any website, it's important to remember a few things regarding how the image is saved.
1. If there are no transparent parts of the image that need to display on anything but a solid background, use a web-quality jpg.
- Click File.
- Select Save for Web & Devices (Alt + Ctrl + Shift + S).
- Select JPEG.
- Lower the quality until a noticeable difference in the image is visible.
2. If the image is large, has transparent portions, and has to display over an image background, export the image as an 8-bit png
- Open the .png image.
- Navigate to the Optimize window (Window > Optimize or F6).
- Select PNG 8.
- Select a transparent Matte.
- Select Alpha Transparency.