I have to admit Steven that the difference between the three words in upper or lower case escapes me. I must have read the instruction manual a dozen times over the last week and I still don't understand how the system works. Juicebox as a product is brilliant but when "LARGE" and "large" become importantly different I struggle.
JuiceboxBuilder-Pro is capable of generating three different image sizes (so that Juicebox can display the most appropriate size depending on the device being used to view the gallery). We call these 3 sizes SMALL, MEDIUM and LARGE in the 'Set Image Sizes' control panel as the SMALL set of images will be used when the gallery is displayed on small screen devices (mobile devices) and the LARGE set of images will be used when the gallery is displayed on large screen devices (desktop computers). This is not strictly true (the actual logic is noted here) but it gives you an idea what the 3 images sizes are for. There is no need to display a LARGE image (wasting bandwidth and taking longer to load) when a SMALL image will do.
For example when you and I first met less than two weeks ago you pointed me to a screen mode called Small so I could fill my thumbnail page with nothing but thumbs.
I suggested using Small Screen Mode as it is the only way to have thumbnails and main images on separate pages. However, as I have mentioned, Small Screen Mode was designed for small screen devices (to give the main images more room to be displayed on mobile devices where screen real estate is usually limited) which is why SMALL images will be used if they have been generated.
Take another look at these two support sections and hopefully things will fall into place.
Screen Modes: https://www.juicebox.net/tour/gallery/#screen-modes
Multi-Size Image Support: https://www.juicebox.net/support/multisize/
Can you take a look at these two snips and let me know if I have chosen the best settings for my needs?
Your screenshots show that:
(1) The 'Resize Images' checkbox is deselected
(2) The 'Use Watermark' checkbox is selected
As the 'Resize Images' checkbox is deselected, JuiceboxBuilder-Pro will not resize your source images (so the 'Max Width' and 'Max Height' in the 'Set Image Sizes' control panel are ignored).
However, because the 'Use Watermark' checkbox is selected, JuiceboxBuilder-Pro does need to process the images (to add the watermark) so the 'Quality' setting is used when the new watermarked images are generated.
If you find that your gallery images are not of a high enough quality, then try increasing the 'Quality' from its default value of 80 to something higher. Maybe try 90 instead. Above 90, the law of diminishing returns usually kicks in, giving little visual quality improvement but increasing the filesize significantly. However, trial and error will likely allow you to achieve the best balance between quality and filesize.
Also, as the the 'Resize Images' checkbox is deselected, there will be only one set of images in your gallery (technically the MEDIUM images but don't worry about what they are called... they can be whatever resolution you want them to be) which will be used under all circumstances.