1- If you turn the construct 180 degrees on the Y-axis the seam in the sky part moves to the positive Z-axis, behinf the default camera position and therefore becomes less irritating. You can slap on a panoramic image. Consequence is the ground texture goes ' south-up'.

2- 'Create perspective UV' in the group editor works again. This gives you another way to apply your favourite image as a background passing across the ground/background separation. The good thing with digital cameras is the images come with the EXIF data that give focal length so you can work out your settings. Remember focal length of Poser cameras relates to traditional 35 mm analog and the width of the viewport. Your EXIF data should give actual focal length of the lens used.