It depends a little on the type of image. There are three different types of images inside of Stacks – so depending on the what/where some images have a bit more customization than others.
Here’s the short answer: try double clicking. That works on most image stacks.
If that doesn’t work, then it’s probably a site image – and you can edit the filename in the RapidWeaver Resources window.
But here’s the long answer with lots of fun details…
The new way – Site Images
You can tell the image is a Site Image because it will say “Site Image” in the title-bubble of the stack.
In Stacks 4 we introduced Site Images. Site Images link to a RapidWeaver project resource. This is a huge step up from how we did things previously. It allows one single image to be shared across many pages, only be uploaded a single time to the central project resources, and only need to be downloaded once by your visitors.
To edit the details of a Site Image you should edit the project resource itself.
Open the Resources window in RapidWeaver and Ctl-Click on the images there.
Not many frameworks or 3rd party stacks are using Site Images yet – so if you’re using a Foundry, then there’s a good chance you’re NOT using a Site Image.
The old way – Image Stack
Old images are part of the page (instead of being part of the site itself). You can edit their properties simply by double clicking them. The properties, like the file name, and export format can be changed there.
There is one exception – GIF images. RapidWeaver doesn’t have a built-in GIF image exporter – so with GIF images we just have to leave them alone.
Image Properties – In the sidebar
Some stacks also have image properties – a place where you can drop an image into the sidebar settings along with all their other settings. Image properties are designed to be as hands-free and automatic as possible. Stacks exports them in a way that ensures their file-names never overlap (even if you drop the images with the same name into many properties) and always save in their original size and format.
Hopefully that little explainer helps to clear it up a bit.