Below are  a few examples of 300 X 204 (pixels) .PNG files with a transparent background.  Yours should be the EXACT same dimension/file type.

TIP: This image should give a little intro about what your app is about. 

TIP: Below this image, the text “Click the button below to begin.” will be displayed (so you don’t need to add that to this image.

Example 1:

Example 2:

Example 3:

Example 4: