There can be various reasons why your gallery picture is not being displayed in item lists even after a few hours of when you created your listing. The basic reason can be that the picture you submitted was in the unsupported format. The formats that support are JPEG and GIF. The server you are using play quite an important part in this. Other reason can be that the server responsible for hosting your picture might be in the non-working state when the system of eBay attempted to capture your picture for the gallery.
Most of the errors in computer related jobs are the result of misspelling. While creating your listing along with gallery picture find out whether the URL or the Web address you have submitted was not misspelled or had any error in it. Using the item number you can check your image and then try to retype the web address where your gallery photo might be available.
The image might be over-sized and there is extra space around the item in the image. For this you can crop your image to reduce the extra space and re do the procedure for submission. eBay has an option for you in this also. For easy hosting of your gallery picture you may use the