When buyers browse categories or search for items, they see items with Gallery pictures directly in search results. Adding a Gallery picture may increase your chances of a successful sale. Items with a Gallery picture sell for an average of 14% more than those without one.
The first three Gallery pictures are free. The first picture is shown to buyers in the search result pages.

Adding a Gallery picture to your listing
Using eBay Picture Services:
Include at least one picture in your listing.
In the Pictures section of the Sell Your Item form, the "Gallery picture" check box is pre-selected for you.
Using self-hosted pictures:
Type or paste the web address of your picture into the box provided on the listing form. Supported picture formats are JPG, GIF, PNG, BMP, and TIF. All formats are converted to JPG when saved on eBay.
Note: The recommended size for the picture you submit is 640 pixels on the longest side. Source pictures with smaller dimensions can be used, but may result in lower quality Gallery pictures.
In the Pictures section of the Sell Your Item form, the "Gallery picture" check box is pre-selected for you.
See the listing upgrade section of the Fees page for more information on the cost of this listing upgrade.
Note: The picture you submit when you add Gallery is automatically sized to 80 pixels on the longest side in List View and 96 pixels in Picture Gallery view. Gallery pictures are usually generated within minutes of being submitted, but may take up to several hours at peak times.