When you create ads in PlugRush in order to buy Plug Traffic, you have to provide a thumbnail. This thumbnail should be as high quality as possible to make sure it attracts maximum clicks from visitors in the network. There is no max size to the thumbnails, but, you should make sure it is at least 180x135 pixels (regular ads) or 180x270 pixels (gallery ads). It is recommended that regular ads thumbnails have a 4:3 aspect ratio while gallery ads have a 2:3 aspect ratio. Thumbnails below these minimum sizes will be rejected.