Try to take the screenshot of the item against a dark background (perhaps by adjusting your camera angle to be largely covered by a blank Ad Sign, or a a dark wall indoors/at night OR a very bright uniformly coloured background (the desirability of option A or B can vary depending on the item) and then paste the screenshot into an image editing tool (such as Paint.NET), use the Magic Wand tool to eliminate the backdrop of the item in your screenshot, crop the screenshot to the exact size of the item in question, save as a .png, and upload it to EntropiaWiki. It may need to be uploaded separately and then have its' ID associated with the entity you desire to associate it with in some cases, this can be done by going to http://www.entropiawiki.com/Gallery.aspx and clicking "Add Image".