Pictures can portray emotions, situations, settings, and background far more concisely and often more accurately than words can. Especially in moments of action, pictures do not lie, pictures do not conceal the truth or sugar coat it, pictures describe exactly what happened.
Depends on the perspective. Sometimes, and image can impact an individual more than words ever could. On the other hand, others hear what's being said, but disregard the image if it doesn't quite convey the impact needed. I guess the real question here would be as to how the image itself is portrayed. One that is poorly depicted will hold little, if any, impact at all. While one that is more "detailed" in it's depiction will often attract more attention.
Then there's also the question of the content of said picture, and said statement. Does the topic cover social concerns? Or Personal? Will the content appeal to a mass audience, or just to a select few? But I guess I kinda brought myself in a circle. >.>
I think the quotes are more teaching people to see that pictures and other stuff that need all your senses to appreciate or understand is more than just words as you only hear them, but you don't really HEAR and understand the words.
Pictures clearly speak louder then words. Is it easier to feel the emotions of a story on a scene or seen it for yourself before your eyes? The true emotions and feelings shown. Whether it be joy, sadness, pain, love, or suffering. That's why actions speak louder then words, you can talk you're going to do something but showing you can or did is far more solid then words alone. The same general idea can be applied to pictures and words. Words can leave doubt but seeing it provides more proof then words alone. Such as illusions, most are fooled because they see it but you describe it, they don't fully believe it or not as close as if they saw it. So again, apply that to pictures once more.
Sometimes things and ideas cannot be said in words, thus people express themselves in pictures.
Words...can be confusing, especially when one cannot read. Poems, for instance, are hard to analyze sometimes because of the many symbolisms and themes. A person can look at a picture and find many things.