The reason that this is happening is that there are no filters set up for that content type. To resolve this, follow these steps:
  1. Click on Content Types
  2. From the dropdown, select Homepage
  3. From the Fields box, select Edit
  4. Next to Banner image, right click on the dropdown of choices
  5. Click on Select Field Properties
  6. Select New Filter
  7. When the New Content Filter window pops up, click Add Folder
  8. Expand assets
  9. Expand images
  10. Select the appropriate folder and click OK
  11. The box for folders should not populate with the correct path. Click OK

These images will now appear as options for your Banner Image.