Almost. Even if the distinction is not that sharp and maybe some people would disagree, I'd say that "obraz" is rather a painting, and "obrazek" is a picture.
Thank you for your explanation. And how would you say 'a painting of a country'? 'Obraz kraju'?
I guess so, but that sounds metaphoric, more like "the country's depiction" for example in a book or a movie. Well I guess that's because, well... how can one paint a country, literally? Only the way it looks on the map...