Text (or language) can convey thoughts and arguments. Images cannot (unless there is text in the picture).
To explore this concept we first read the following text:
"The sky is not blue. The fact is, of all the colors in the visible spectrum of the sun’s light, the only color the atmosphere reflects is blue. It absorbs all the other colors. Therefore, the sky is every color BUT blue."
The text is putting forth an idea that you could argue for or against. If I asked you to argue against it, you could do it by critiquing any one of its assertions.
Next we looked at this painting by Artemisia Gentileschi.

We looked at some other images as well such as: (you can click to enlarge them)



Then we went back to the beginning and I started to give you background information on each image. For example, with the Gentileschi painting, I asked what its argument would be if you found out that the artist had been raped in adolescence. Suddenly the interpretations changed. The painting was suddenly arguing "Men are pigs." Some class members thought that the artist was getting her revenge on the man who raped her.
The same thing happened with each image, the more information I gave you, the more your interpretations changed.
At one point I asked a class member to argue against one of the images. The most common response was, "Argue against what?" It was a very good question. Images contain no arguments. Any argument an image might inspire must be created by the viewer and formed into language.
This is an essential idea to understand as we head into mass media studies: text (or language) can put forth arguments, images can not.
In other words, a picture may be worth a thousand words, but the viewer is the one who must make those words.