I actually know a bit of backstory about this photo - it was a series on child labor in the south, and these are photos of oyster shuckers for the Maggioni Canning Co. around 1911.

I’m assuming shucking oysters are rough on the hands, so it could be wounds, but it also looks like crusted-on dirt, so I’m not sure.

Here’s another photo where you can see their hands a bit better:

And here’s the original untouched photo:

Courtesy of the Library of Congress archives