I’ve gotten several requests for more information about photosensitivity since this happened, so I spoke with Andy Hunt at Pragmatic Bookshelf about the issue. Andy reacted similarly to the problem and we’ve decided that, as a public service, we’re going to release Tip 27: It’s Not Polite to Flash the Audience from Design Accessible Web Sites free of charge. Reading back through the tip, however, I wish I had covered the issue more deeply than I did—the tip introduces the idea of photosensitivity and a couple of tools for testing video, but I didn’t go into other kinds of content like I should have. So let’s look at the issues of photosensitivity and user-submitted content like message forums.
The first route of defense for the site developer or administrator is to
content in user posts. This, of course, is a good idea anyway because of the security risks of
allowing your users access to these tags. That simple filtering takes care of rogue Flash, Java,
For whatever reason, animated GIFs still seem to be popular in the “still thinking digital
watches are a pretty neat idea” parts of the web (with all due apologies to Douglas
Adams)—so there is still significant demand for browsers to default to supporting repeated
GIF animation. Blocking animated GIFs in user submitted content is difficult at best. The only
real options are:
<img>entirely: This isn’t appropriate to many forums because it unnecessarily limits discourse.
- Filter the
*.gif: This doesn’t really work either. An off-site url to a GIF file can easily leave out the file extension but send a correct GIF mime type.
- Only allow uploaded images and
src=references to your site: This isn’t feasible for technical (do we want to store a ton of graphics for our message boards?) and liability (they uploaded a picture of a giraffe doing what??) reasons.
- Moderate all image submissions: If you have enough moderators to handle it, this might be possible, but most of us don't and it’s still an impractical approach.
At the end of the day, only the last solution addresses non-animated images with potentially seizure-inducing patterns. As developers, there are some things that we can’t easily address, and it may be that the best we can do is to provide a notice reminding our users that the forums contain user-submitted content which has not been fully vetted for accessibility—this is generally a nice thing to do when you don't have absolute control over the content anyway.
This means that site administrators need to be aware of problem images that appear on their sites and remove them as quickly as possible and users with photosensitivity will need to be careful, as in public spaces, to be aware that certain patterns may show up that could be a potential threat to them.
For users with photosensitivity concerns, there are also ways for you to configure your web browser to minimize your personal risk from animated content:
- Firefox: The Content tab preferences has checkboxes for enabling or disabling Java
off Flash while leaving placeholders that allow you to start the content if you wish.
Changing the animated GIF settings in Firefox, however, is unnecessarily painful, requiring
you to alter the value of
about:config. If you’ve never done this sort of thing in Firefox, more detailed instructions are available at mozillaZine.
- Internet Explorer: The No Flash! tool allows you to easily turn off Flash, Script, and GIF animations. Turning off Java in IE is somewhat more involved but Microsoft provides directions at their support site.