Depends on unreleased version of babl
gnome-photos currently depends on babl-0.1
pkg-config package, which is only available in git master (and not in the latest 0.1.98). As babl doesn't follow the gnome release cycle, you cannot depend on the git version.
Essentially, I'm asking to revert !248 (merged). However since it seems really trivial (i.e. no actual changes to the code) a better solution would be to check for both the old and new pkg-config name.
Edited by Abderrahim Kitouni