I've spent about four years as a medical tech working with epilepsy in a neurology lab. Sorry, but this just gets up my nose.
Please stop using 'flashing images' as a way to co-opt epileptics into defense of the issue-of-the-day (that's the only thing I can think of as to why you included it). Yes, some epileptics do respond to flashing images (~15% have the kind required, less actually respond), but the parameters are pretty tight for the bulk of them. The kind of flashing that can trigger a seizure is also monumentally irritating to regular users, and generally hasn't been used since the 90s.
I spent four years in a full-time job where I sat in the dark flashing lights at epileptic and suspected epileptic patients, 4-6 times a day while recording EEG, so I've got a reasonable subjective feel for the kind of flashing that fires it off. I've spent a lot of time on the web, too, and the only thing that even comes close in general use are the flashing-style 'you are the 999999th visitor' ads, and even then they usually subtend too small an arc of the visual field.
For the record, the usual range for photosensitive epileptics to respond to flashing images or lights is 12-20Hz, with a peak different for each patient and with some rolloff at each end. Above 25Hz epileptic responses are extremely rare - I've not personally seen one, but they do exist.
Yes, there are some epileptics that can have a seizure from a single camera flash, and I've seen them, but they're reasonably rare amongst flash-responsive epileptics (themselves an uncommon group). I've also heard of an epileptic whose trigger was orange circles - not orange other shapes, or other coloured circles (anything can be a trigger for a seizure). At what point do you set the bar for rarity?
Sorry, but it gets up my nose - almost every time I've seen someone 'defend epileptics' online, they don't actually know much about epilepsy, and seem more to be using common mythology about epilepsy in order to co-opt the illness to strengthen a point being made.
Of course, two other common forms of trigger, depending on the kind of epilepsy, are stress and hyperventilation (strictly speaking, these are less triggers and more threshold-to-event reducers). In this case, one could argue that frustrating site design works against epileptics...