The Image linking section, under Album > Settings > Pages, seems to be a source of confusion for some users.
Let's start off by explaining what it does not mean. This is not a place to tell jAlbum what images to use to create the album. jAlbum uses whatever images you add to the album project. If those are image files directly from your digital camera, that's what jAlbum uses to build the album. If those are image files that you've done some tweaking to, in PhotoShop or Picasa for example, those tweaked images are what jAlbum uses to build the album.
Instead, image linking defines which version of the image appears when a visitor clicks a thumbnail (i.e., what the thumbnail links to), and what version(s) of your images ends up in the completed album. jAlbum can use the images you feed it directly, without any further changes, or it can process those images to make them more web-friendly (smaller files, for example), or to do more image manipulation like adding a watermark, adding borders, cropping, and so on.
If you check Link to scaled-down images only, the only images included in the final album will be those that jAlbum has reduced to fit in the image bounds you've set under Album > Settings > Images > Image bounds. jAlbum will also apply whatever image filters you've chosen, either in the image editing window (on the right when you double-click a thumbnail) or by using skin settings or user variables. The images that land in the album end up being much smaller files than typical digital originals (like maybe 300KB vs. 4MB). So, when a visitor clicks on a thumbnail, the image he sees will be that scaled-down version. Given the resolution of monitors, the quality will be excellent, as long as you've chosen the Smooth scaling method, and JPEG Quality of 75%-85%.
If you check Link to originals, jAlbum won't do any scaling - in fact, it won't touch your original images even if, for example, you have told jAlbum to use filters on the images - those requests will be ignored. It will simply use the image you have added to the project in the final album. When a visitor clicks on a thumbnail, it will display the original image that you have fed into jAlbum, unaltered. This is the choice for someone who's doing all of his image processing outside of jAlbum, including scaling it down to a manageable size. If, for example, you use an application like Lightroom to work with RAW images from the camera, you could export the final result as a resized JPG, and then tell jAlbum to use that image without any further processing.
You can also choose this option just for selected images. You could choose Link to scaled-down images only for the album, but then right-click on a specific image and choose Use original. For that one image, the image that's used in the album will be your untouched original.
If you actually linked to the originals that come out of your camera, without any resizing, your site visitors would have a pretty miserable experience. Each time they clicked on a thumbnail, they'd have to wait while the page downloaded the next 4MB image file. Even with a good broadband connection, it would entail a lot of "Loading" waits. And if you didn't scale down the images yourself, and then used a skin that doesn't adapt the display size of each image to the browser window, your visitor would often be looking at about one-quarter of the image, with scrollbars.
The Link to originals via scaled images choice is largely meaningless in many skins. Let's look at two that actually do make use of it. First example, Turtle. With that option, when a visitor clicks on a thumbnail, it brings up the scaled-down image. In the caption area, however, there will be a download icon that, when clicked, provides him with the full-sized original image. Second example, in Matrix, you can choose that option, then have Matrix put an Open image in new window button in the caption area. So, when a visitor clicks on the thumbnail, it shows him the scaled-down, manageably-sized image. If he then clicks on the button, it opens a new tab or window, and displays the full-sized original. In short, it's up to the skin developer to decide whether to make use of that option, and how to do so. Some skins use the linked original, most do not - only experimenting with a given skin's options will tell you what that skin does.
Choosing the Link to originals via scaled images option does result in the original images being included in the output directory, so they'll get uploaded to the server, whether the album is actually using them for anything or not.
This is another option that can be chosen for selected images. Again, you could choose Link to scaled-down images only for the album, but then right-click on a specific image and choose Include original. Now, when you make the album, jAlbum will scale down all the images, and those are what the visitor will get when he clicks on a thumbnail. But the full-sized original of that one image will also be included in the output directory. In Matrix, for example, if you have an Open image in new window button on that image, clicking it will bring up the full-sized original in a new tab or window. Again, how to make use of this feature is up to the skin developer.
The Link to hi-res via scaled images choice is almost the same as Link to originals via scaled images, except that instead of including the actual, full-sized original images, jAlbum will include its own hi-res images. These are scaled to 2048x2048 pixels, which usually makes the files smaller and more manageable than the full-sized originals from the camera, while not losing image quality. Like the Link to originals via scaled images choice, this does not have much effect with most skins, though again, it does mean that the hi-res images will be created, and will be uploaded with the album. No jAlbum filters (watermarks, etc.) are applied to the hi-res images.
A word about the Copy originals if needed field. With the current version of jAlbum, it's best to leave it checked all the time, regardless of the linking method you've chosen. And if you're including videos in your album project, this box should always remain checked.
Copy originals gets checked automatically if you choose the Link to originals box, since if you're going to use the originals in the finished album, it's usually a safe bet that you want to copy those originals from wherever you have them scattered all over your PC to the final album's output directory. That way, they'll get uploaded when you publish your album, and will automatically be available for display in the album. (Strangely, however, Copy originals if needed does not automatically get checked if you choose Link to originals via scaled images.)
One of the only situations in which it makes sense not to choose this option is if you're running jAlbum on your server, in which case the originals are already where they need to be - there's no reason to copy them again. Similarly, if you're uploading your album to a server directory that already contains the originals, there's no need to copy them to the output and upload them.
If you've chosen Link to scaled-down images only, your original images won't be copied to the output directory, even if Copy originals if needed is checked, unless you have specifically chosen to include the originals for one or more of the images in the album (the "right-click on a thumbnail" options described above). Copy originals if needed will never put unnecessary original images in the output directory.
So, you should always leave Copy originals if needed checked - your originals will be copied to the output directory only if they're actually needed for the album.
Edited by: jGromit on 27-Oct-2017, to make wording correspond to current user interface.