Hello Israel,

I put together a sample that achieves what you are looking for by using a Creation Filter. With this logic you can provide a new image within an ImageUIElement and add it as a child of the Ribbon area. 

public void AfterCreateChildElements(UIElement parent)
{

// Check for the RibbonPagerArea             
if (parent is RibbonTabPageUIElement)    
         {
              Image newImage = RibbonGroupAreaSample.Properties.Resources.Image;   
              ImageUIElement aImageUIElement = (ImageUIElement)parent.GetDescendant(typeof(ImageUIElement));    

             if (aImageUIElement == null)             
                {                     
                 //Create a New ImageUIElement                                    
                    aImageUIElement = new ImageUIElement(parent, newImage);           
                }            

                  parent.ChildElements.Add(aImageUIElement);
                //Size and position the new image to the far right of the group area with padding as necessary.      
                aImageUIElement.Rect = new Rectangle(parent.Rect.Width - newImage.Width + 10, parent.Rect.Y, parent.Rect.Width,

For more details please refer to my sample attached.