To add this to your bookmarks bar, you can either drag the above snippet to your Safari bookmarks bar on OS X and then sync your iDevices (assuming you have bookmark sync enabled), or you can do the following:
- Bookmark the current page on your iDevice, and change the title when you save it to something like “Alt Text”.
- Copy the entire snippet as it appears above.
- Edit the bookmark in Mobile Safari and paste the snippet into the address field.
To use it, just tap the bookmarklet and then tap the image you want to see alt text for. The script will insert the alt text directly before the image in the page. Enjoy!
Based on the script I found here on Macworld’s hints site.