This article will show you how to display an alternate image on your grid item from your Custom Meta Data
Step 1. Create an "Image Type" Custom Meta Data
Step 2. In your posts, upload an image into the "Custom Image" Meta Data
Step 3. Edit the Grid Skin
Step 4: Create a new Layer and select Text/HTML as Layer Source.
Step 5. Replace the Layer Texts with the HTML code below in the "Text/HTML" source