How many woodpeckers visit the garden?

My new woodpecker feeder is proving very popular, with many visits each day.  Apart from telling males from females, identifying individual birds is not easy.  It is difficult to tell whether there is one woodpecker who keeps coming back all the time, or lots of birds each making one visit, or (most likely) several birds making several visits.  I do see up to three at a time in the garden, chasing each other off the food.

The camera allows a very clear view of the birds and they tend to sit on the feeder in the same position in the same attitude.

These four photos are of birds visiting on the same afternoon but it is difficult to tell how many individuals are here.  I suspect the top right and bottom left may be the same bird but can't be sure.  The other two I think are different.

One difficulty is that the feathers move around a bit as the bird moves, changing the pattern of black and white slightly. Also some of the birds may be related - father and sons or brothers - and they might be expected to resemble each other more than unrelated birds.

I haven't been able to find anything written on which physical features are likely to vary between individual birds.  The pattern of black and white on the shoulder is one possibility.  The shape of the white cheek patch and the pattern around the eye are others.

This bird clearly has black feathers in front of the eye.

This one has white in front of the eye.

Here are two photos of females taken on different days but I think they are the same bird (or closely related).  The first photo is clearer (better light and closer zoom).

A few more photos all taken on the same day (different from above).  First four consecutive males.  How many individuals?

And two females, unfortunately in slightly different poses.  But are they the same bird?  Probably not.

I think the only way to resolve it would be for me to train as a ringer, colour ring the birds, and then photograph them as well.  Maybe I'll just stick to enjoying watching them.  If you have any ideas or suggestions please leave a comment.