What kind of image can I use for the Player background?

From Avacast Support

What kind of image can I use for the Player background?

The background that appears in the Player should follow certain specifications to ensure that it will appear properly.

Image size: The image you set will scale to fit whatever size the window size of the Player, but the optimal starting size is 750 x 563.

Format: Background images should be JPEG format (Flash SWF will also work, but is not recommended due to potential performance issues). Do not use a progressive JPEG, or else it will not appear in the Flash Player. Note that GIF is no longer supported since the Flash version of the Player was introduced in version 4.0.1

An image works best when its file size is as small as possible (in consideration of your end users) and the design is simple (so that the background works well with other Player components; complicated designs can reduce readability or usability).

Avoid pure white (#FFFFFF) in a background image, because those areas may become transparent in the Shockwave Player. If white is used at the edge of the image, that portion of the image will be cropped off in the Shockwave Player. You can use a almost-white color instead (e.g. #FEFEFE), and most people will never notice the difference.