The basic method you can use is to put various filtered portals on a form view layout. The portal need not be more than one row tall. I've used this method to show invoice counts on a zip code map so that looking at the map shows you how many customers from each zipcode patronized our business over a user selected date range.
I would assume that these assignments can change from race event to race event so I'll suggest a third table on which to base your report:
RaceEvent::EventID = Track::EventID
Track::position = Workers::assignment.
Now create a from view layout and paste or insert your jpeg image on to it.
Add one row portals to Track at each assignment location. Let's say you want to show the worker assigned to position "ABC"...
Give the portal this filter expression:
Workers::assignment = "ABC"
The portals will be identical except for the filter expression, so once you have one working, you can copy and paste it, but open portal set up to update the filter expression for each position.