vtkOpenGLImageMapper doesn't respect vtkProperty2D::DisplayLocation
The OpenGL2 implementation of vtkOpenGLImageMapper doesn't respect the value of vtkProperty2D::DisplayLocation for vtkActor2D objects. Instead, it behaves as if the DisplayLocation is always VTK_FOREGROUND_LOCATION.
The OpenGL implementation of vtkOpenGLImageMapper checks the DisplayLocation here: https://gitlab.kitware.com/vtk/vtk/blob/54b4469ca9c6f19bc76568553ce51b50e1bce09e/Rendering/OpenGL/vtkOpenGLImageMapper.cxx#L685-686
This issue manifests in Slicer when using the OpenGL2 backend; see http://www.na-mic.org/Bug/view.php?id=4251.
See attached file for an example that demonstrates the problem: