There is an image that is not a banner on the signin page that I don't easily see where to change it. Where is this image?
Please be sure to state your theme for things as sometimes it is theme related. Here are a few tutorials that will help:
https://community.socialengine.com/blogs/597/72/elpis-theme
https://community.socialengine.com/blogs/597/92/changing-the-log-in-image
https://community.socialengine.com/blogs/597/124/inspira-theme
More than likely, the second tutorial above is the one you need.
Let me know if that doesn't help. I think, from your image, you are using Inspira. That second tutorial should work for it but I can go check my own site and see, if needed.