How can one picture belongs different galleries?
For example, there are two galleries. I want to avoid loading the image twice (in two galleries) but it shown (included) in the first and second gallery.
This is not possible in NextGen gallery.
You have to upload the image into each folder, as NextGen gallery works with file structures, not with database entries for retrieving the images.
You can use the
This include images with IDs: 1, 2 31, and 6. And on the second post:
This include images 7, 12, 45 and 6.
As of WP 3.5, the