@mauve This looks like it might be a graphviz diagram...
SVG output instead of a PNG might help a little, but perhaps you could try publishing the diagram source code - only good for very techy users, but at least it's textual.
@sundew Yeah, the labels are legible but IIRC the edges aren't in the accessibility tree. Have you tried graphviz with screen readers before by any chance?
@mauve I've used graphviz a lot, but not in the context of accessibility I'm afraid.