Can I say that a painting or a photograph is polemical?

You have only to consider one person's opinion about what the 10 most controversial artworks in modern times are, to appreciate how polemical and disputatious any work of symbolic art can be, whether it be a painting or a sculpture, a billboard or a broadside (aka broadsheet), a newspaper headline or a magazine cover, or a photograph or a movie, to name but a few media.

What they all have in common is the power of symbols, and there is tremendous, world-changing power, potentially at least, in every mode of communication and in any combination of modes. Take, for example, a single photograph of a young Vietnamese girl running naked down the street with a look of terror on her face, after her village was napalmed by American forces in her country, which left her scarred for life.

Such was the picture taken by a photographic journalist during the Viet Nam war:

Frankly, words on the page are not needed to describe the horrors of war as seen in that photograph.

Let us not, however, minimize the importance of words alone to be polemical and disputatious. Words and pictures, however, often complement each other, and in combination accomplish more than they could individually, as in the following painting of the Spanish king/monarch, Felipe VI:

Translation: Welcome, refugees.

Or how about the following work of art, taken from the same article on the web (viz., "7 Political street art figures and controversial artworks observed globally"):

And finally, here is an abstract of an article written by Jens E. Kjeldsen about the rhetorical power of pictures:

Some forms of argumentation are best performed through words. However, there are also some forms of argumentation that may be best presented visually. Thus, this paper examines the virtues of visual argumentation. What makes visual argumentation distinct from verbal argumentation? What aspects of visual argumentation may be considered especially beneficial?

So, is a picture worth a thousand words? Potentially it can virtually bypass verbiage and change a person's mind. That is the nature of rhetorical reality, in words and pictures.