Right now libplybootsplash pulls in libpng unconditionally. This means on very bare installs, libpng will get pulled in for no good reason.
We should probably split libplybootsplash into two libraries and only link to the second library when a graphical plugin is installed. Alternatively, we could make ply-image like ply-label and have a plugin that's loaded at run time.
I fixed this up a while ago.