Zoom Image
Store two images in two different resolutions (e.g. preview image and full resolution). By clicking on the thumbnail, the user gets an enlarged view of the image (or the second image).
Settings
Preview image (thumb)
The image number selected here displays the small preview image. By clicking on the image, the high-resolution image is activated as a layer.
High-resolution image (highres)
This high-resolution image (defined by the image ID (iid)) should have a higher resolution than the previous image.