It would be nice if there is/was an active project which has the same feature-set.
Gallery or Menalto Gallery is an open source project enabling management and publication of digital photographs and other media through a PHP-enabled web server.
As a drop-in replacement it would need to be able to run on -
a. Apache2.4.x - latest in debian is 2.4.23
nginx would also be ok but apache preferred.
b. MySQL 5.x - latest in debian is 5.6.30-1
Postgresql may also be possible but mysql preferred.
c. PHP version 7.0.x - latest in debian is 7.0.12-1
Essential feature-set it would have to have -
Photo manipulation includes automatic thumbnails, resizing, rotation, and flipping, among other things.
Albums can be organized hierarchically and individually controlled by administrators or privileged users
The code needs to be foss/open-source license which is used/compatible with Debian Main - See https://www.debian.org/legal/licenses/
The project should be a mature project having a few public installations to see and feel how it works.
Should be a public hosted repository either on github or their own personal repository. Bzr or/and mercurial also works.
There should be some history of accepting patches from third-parties.
Should be an active project.
While it may or may not be possible to have all the above points, if they are any projects closer to the points above, please share those with links.