Here’s something you see a lot with banner stands (often called pull up, retractable, or roll up banners). If you get much light behind the banner, you’ll see the shadow of the pole. If you put the banner stand in front of a window this is especially noticeable, in this case it was simply a light fixture behind the banner stand.
The simple solution is to get a banner stand that uses a light blocking film for the banner. We use this on both our standard and premium banner stands.
The light blocking layer is a black layer of material behind the white face on which the image is printed. It make the banner material opaque. Obviously this is a more expensive material, but it can be worth it! You get a banner stand that can be used anywhere.