It is not possible to set exact sizes for images in a Juicebox-Pro gallery. The size of the image area within a gallery will depend on a number of factors:
(1) The size of the user's browser window.
(2) Whether or not space is reserved in the gallery for other elements (such as thumbnails, captions, gallery title).
If you use SimpleViewer-Pro and use a Fixed Layout, you can specify exact dimensions for the gallery's image area via the imageAreaWidth and imageAreaHeight configuration options.
You can hide thumbnails in a Juicebox-Pro gallery by setting showThumbsOnLoad="FALSE" and showSmallThumbsOnLoad="FALSE". (You can also hide the Thumbnail Button (to prevent users from displaying thumbnails) by setting showThumbsButton="FALSE" and showSmallThumbsButton="FALSE".)
For a SimpleViewer-Pro gallery, set thumbPosition="NONE".
You can hide captions in a Juicebox-Pro gallery by setting captionPosition="NONE".
For a SimpleViewer-Pro gallery, set captionPosition="NONE".
Please feel free to post suggestions for future versions of Showkase in the Feature Requests forum thread.
It keeps them all together and ensures that they are not overlooked.