On some of the websites I have built, I have customised the template and added an area to recognise sponsors in the footer. This has worked reasonably well, but in this age of funding depletion and shifting loyalties, funder’s which were often considered to be regular supporters will change. So now your website is out of date.
I generally get requests to help in this area. It is more complex than conventional editing. One way to handle this is to locate the image in the media library which is normally a composite of several images, delete it and replace it with a file of the same name and size. However this does not work if the media library is split into directories on a monthly basis. (You may not be aware of this, but the directory structure in WordPress is either a single directory or multiple directories based on Month and Year.)
Other complications
As I start to move over to Responsive (mobile friendly) sites, images generally scale but text stays constant as the width of the screen changes. If an image on your site has a live (clickable) area, then this may move as the image scales. If you look at the image below, the letter A is “live” but the letter “B” is not. This is because I have created an area which is invisible but makes part of the image support a live link. These may shift as the width of a page is rendered.
A solution
One way around this problem is to have a full width image at the bottom of your home page on your site. On this image you place the various logos of your supporters. You make the whole image a clickable link, and set the target destination to a page within your site which specifically recognises sponsors and supporters. (A friends page for example).
In the example above the whole image is set up as a clickable link. As you move your cursor over the whole image it changes to a hand (On a PC).
If you click on it, it will take you to a special page. On this page you could list each sponsor and carry a link back to their website to demonstrate your support.