Does anyone know whether it is possible to send QR codes to event participants via CiviSMS? A client wants us to send participant's QR codes to their mobiles.
It doesn't look like the Twilio extension supports MMS at the moment and probably not Clickatell either but you can text the recipient the link to the QR code. It looks like you would need a public link anyway for Twilio's api if the extension supported it.
As mentioned in my comment to Demerit's answer I successfully achieved my objective to send a QR code to an event participant's phone (albeit the URL and not the image).
I installed the Clickatell extension for CiviSMS and the QR Code Checkin extension to generate the emails or SMSs to send the QR Code or its URL to event participants.
The instructions to set up the Clickatell extension at https://docs.civicrm.org/user/en/latest/sms-text-messaging/set-up/ are outdated but it was not hard to set it up.
The QR code extension was easy to set up, but don't forget to manually set the required permissions in your CRM (Drupal in my case). The extension provides a handy couple of tokens that can be easily included in an email or SMS.
The downside of the QR Code extension is that it only works on one event at a time. If you have multiple events that run on different days it may be possible to change the 'effective' event (on the event page) before sending QR codes and again during checkin. I haven't tested this.
Below is an example of the test SMS I generated.