superheroic, you can link from anything to open a pop-up layer that contains an image, so you could have a Thumbnail to a completely different image.

You can create a Placeholder and then in Web Properties > Placeholder, pick Replace with graphic file.
The file can be anywhere into you local or networked folders.
This will add the image file into a Support folder so that on Publish is is copied into the index_htm_files folder.
If you Export website, the file is added into the index_htm_files folder directly.

If you have a clutch of files you want to refer to from an Images sub-folder, you add the Images folder with images directly into the Support Folder.
Read https://www.talkgraphics.com/showthr...Support-Folder.

Finally, if you already have a separate PoshImages folder uploaded, you can create a Placeholder and add code into its Body, the simplest being <img src='../PoshFolder/image01.webp' width=100% height=100% />.

What I do is drop the image onto the page, ensure it is in the Support Folder and then use Replace with graphic file.
The image is not then saved with the design XAR/WEB , keeping it small.

Acorn