And maybe they weren’t slaves, maybe it depicting hired field hands!
I had the same idea. When I visited the south for the first time 45 years ago, I saw black people working in fields (I doubt it was cotton but I could be wrong) and was astonished how times hadn’t changed that much.
The more I look at this artwork, the more impressive it seems. The colors seem quite muted. Would love to see a clearer photograph.