How to add a custom footer with image and text above to the Splunk footer?
First, we can't see your image and text in the question. But the easiest way to accomplish this, is to add a HTML panel to the bottom of your dashboard.
In the HTML panel, you can add text and a link to the image. This page in the documentation has an example, but it is the next-to-last example, so scroll down for a bit!
Once you build this dashboard panel, you can save it and then refer to it in many dashboards. I strongly suggest that you put the image in a Splunk app, so that it is local to Splunk. For an example of this (along with another HTML panel example), take a look at this answers post: