The portal image names are stored in subpages of Mô đun:Portal/images, organised by the first letter of the portal name. For example, the first letter of Cổng thông tin:Ngư nghiệp is "N", so the image name is stored at Mô đun:Portal/images/n. If there is an entry for a portal on the correct page then the corresponding image will be shown next to the portal link. If no image is found then Tập tin:Portal-puzzle.svg will be shown instead.

It is also possible to specify aliases for portal images. For example, the code {{Chủ đề|Detroit}} produces the same image as the code {{Chủ đề|Metro Detroit}}. The "Detroit" alias is found on the page Mô đun:Portal/images/aliases.

The image-detection algorithm is case-insensitive. For example, the code {{Chủ đề|Detroit}} will produce the same image as the code {{Chủ đề|detroit}} (although the portal links will be different). Portal names are stored in lower case in the image subpages, and input is converted to lower case before being checked.

To add new images to the list, please 12+2021&section=new make a protected edit request at Template talk:Portal to get an administrator to edit the correct subpage for you. Portal images must be either in the public domain or available under a free license that allows commercial reuse and derivative works; fair-use images are not acceptable.