When you installed Nextgen gallery and added images in wordpress there will be three tables created in database, named as: wp_ngg_album, wp_ngg_gallery and wp_ngg_pictures. using these tables import and export you can easily transfer your gallery images one site to another site.
Export NextGen Albums,Galleries and Pictures Using Phpmyadmin
In first step you need to install nextgen gallery plugin in new site and after that go to your old site which have already gallery. Login to your cpanel and find there phpmyadmin and open your database of new site you will find there three tables of nextgen gallery
after export tables in new site now need to export gallery images in new site.
Transfer NextGen Pictures to New Website
In step 2, download your nextgen gallery image folder and upload it to new installed site. You can find all nextgen gallery picture in wp-content named ‘gallery’ folder, here you can first download this folder and upload it to your new site using cpanel or ftp.
Scan Folder for Images in NextGen Gallery Plugin
Now in final step, need to scan images which you have already upload in your new site. Goto your dashboard in nextgen gallery option and open your gallery here is you did not fine any picture so you have to scan for new images and it will auto scan image from where you upload images in last step.
I hope it will work for you if still have problem you can contact me anytime. for resize NextGen gallery image and album size see post “Resize NextGen Gallery Images and Album Thumbnail