Step 1: Create a theme region and in the content type, add an image field. If your banner is not a slide, restrict the number of images to 1. In case it is a slide, you can use the views_slideshow module.
Step 2: Create new image style for your banner images
Step 3: Create new View. Choose “block” display.
Step 4: In the filter option, choose the desired content type and include a contextual filter for “Content: Nid”
Step 5: Save the view.
Step 6: After this, you can go to your blocks page and add the newly created views block to your new banner region.
When you complete these steps your banner image will be the new image field in your existing content type.