When using the NextGen Gallery, sometimes you have to link the image to a post instead of a larger version. I recently ran into this while working on a site for a client.
The steps after you have installed the NextGen Gallery are:
2. Install the NextGEN custom fields plugin.
3. Navigate back to Manage Gallery and select on the gallery. You’ll see a field to add links (image below – far right)
4. In the custom field put a link to one of your pages, posts, or another site.
5. Go to Plugins > Editor > Switch to NextGEN Gallery in the Drop down Box > and click on nextgen-gallery/view/gallery.php It is near the bottom of the lists. Or FTP direct to gallery.php.
6. Backup the file.
7. Find this:
and change it to this:
You are replacing imageURL with ngg_custom_fields["Link"] so the image links to the URL in your custom field.
8. The ["Link"] will be the name of whatever you named the custom field.
9. It also includes a line that links the alttext or description of the image to the same page.
10. Save. Test.