Some considerations...
1. This is not like publishing a book where you do the work once and then sit back, it is more like publishing a magazine. Once you do the work to generate the index, there is a significant amount of work in maintaining it.
2. Many topics have hundreds of existing pages, making an index page with images would require using thumbnail images since using full sized images would result in an index page which would be exceeding large (slow to load and would be a wall of content). So every time someone makes a new post, you would also have to generate thumbnails for each post.
3. We already have two search features. The custom Google search feature is fast and powerful and it includes images. So for example, if a user wants to search on 'lighthouses' they can easily click on the 'image' tab as shown below.

4. The purpose of having an SQL database behind a forum like this is to NOT have to hand build indexes like this. If time and money are to be invested, then it is best invested in improving the indexing at the SQL level. So the best way to help is to donate money and/or support the advertisers and affiliate links venders.
Don