The ebuild has: -- snip -- RDEPEND=" gtk? ( =x11-libs/gtk+-2* dev-libs/atk dev-libs/glib media-libs/glitz gtk? ( =media-libs/libpng-1.4* ) kde? ( =media-libs/libpng-1.2* ) -- snip -- That's same as: gtk? ( gtk? ( =media-libs/libpng-1.4* ) ) And with USE="-gtk" it doesn't pull in any libpng (except maybe indirectly/implicitly from kdelibs -> qt-gui -> libpng)
In fact, if you grep/objdump/scanelf opera, there's no reference to libpng at all. So Opera is simply using gtk+ or kdelibs/qt-gui and whatever libpng they are using. So the deps for libpng should be simply dropped from opera's ebuild.
Created attachment 237233 [details, diff] fix
Thanks. Fixed.