iMessage group is receiving photo every 2 hours. How do I stop it?

2 weeks ago I sent a photo to 3 friends ( a group) via iMessage. 2 days ago the group started receiving the photo every 2 hours. There is nothing on my iPhone 5s; iPad or MacBook Air indicating any messages that are being sent. I have deleted the group text chain from my phone. They have deleted the group texts as well , bt they keep on reappearing every 2 hours.