1. The picture depicts a girl being betrayed by her best friend. 2. The picture depicts what it is like to grow up in a small town. 3. The picture depicts a typical Christmas in New England. 4. The pictures shows us why it is important to fight for civil rights. 5. The picture reminds us that we should be good so Santa won't bring us coal in our stockings. 6. The picture depicts two puppies chasing a cat around a table. 7. The picture portrays typical colonial style buildings in Massachusetts.

1. A dog chasing a cat is depicted/shown/portrayed in this picture.

Also, you can say: 1. In this picture, a girl is helping her grandmother get out of a car which reminds us of how important it is to be there for our elders. 2. In this picture, a boy has been killed in a car accident because he wasn't wearing his seatbelt; therefore, I believe its message is that you could be dead at any moment so you shouldn't take safety lightly. Sorry, I just realized that I didn't know if you wanted examples of sentences describing what is happening in a picture or ones stating the picture's meaning / message. Anyhow, these two do both. :)

Oh, you can also say "This is a photo of two dogs chasing a cat." and "That is a photo of one of my students riding an Arabian horse at my stable." This is probably the most common way to describe what is happening in a photo in American English. :)