Beautiful skin! A request for having an option of placing the caption or Info panel directly under the main image in the Lightbox (i.e. within an expanded border below the image). On large screens the Info panel with the caption can be very far away from the image.
I believe that would require a major reworking of the lightbox script, so I would not expect such a feature to appear any time soon.
But I believe the real source of your problem is that, in your older material, you're giving jAlbum images that are already too small. Many of them are only 600x400.
Tiger is a responsive skin - it adjusts the size of the image display to suit the monitor. To produce the best display on monitors of all sizes, you need to be giving the project fairly large original images. Normally, you would do all of your image processing outside of jAlbum, but not resize the images. Then tell jAlbum to Link to scaled-down images only, and use image bounds like 1600x750, or even larger.
By choosing Link to originals, as you have, and then giving the project images that are already too small for larger monitors, you're cheating the large monitor visitor.
You could resize outside of jAlbum to larger dimensions, and still tell jAlbum to Link to originals, but I wouldn't do that. As monitor resolution increases and bandwidth limitations disappear, you may find that, two years down the road, you want to scale the images to even larger sizes. But if the project contains only images that have already been resized, jAlbum can't adapt to larger monitors. If your originals are, for example, 6000x4000, you can preserve the freedom to use image bounds of 1600x750 today, but change to 2500x1500 later.
ETA: Using larger originals also makes it possible to get theme images (the ones across the top) that aren't blurry on a large monitor.
BTW, there are a number of other lightbox skins that anchor the caption to the image, rather than the viewport. One of those might suit your needs better. On the jAlbum skins page, check the box for Responsive layout, and take a look at some of the sample albums that the skin developers provide.
Thank you for your extensive reply and the tips! Yes, when I started out in 2005 I wanted to keep file sizes small due to bandwidth limitations. Now I have increased the size to 1080x1080 (or moving to 2160x2160 if using HiDPI). I will take into consideration using large images in the projects from now on, the originals are approx 8256x5504. Increasing the size of the old images would be too much work now, as they are shot in raw and I would need to regenerate them all from the raw files.
Personally I don't mind using a small viewport/lightbox of about 1080x1080 even on a large monitor, but you're right that I won't be taking advantage of the large monitor.
Yes, I've got a lot of older stuff that, in many cases, was scanned from prints or slides, since nothing better was available. In my case, there's literally no way to rescue that material - it is what it is.