Angela Meiers gives a great TED talk about how much 'You Matter.' In it she describes how giving students post it notes with encouraging messages really changes the attitudes and lives of students. Since many of us don't routinely carry Post It notes around with us, a camera enabled phone and Instagram can be the next best thing.
An administrator, whom in my experience often has a county/district issued smartphone, often walks quite a few miles in their shoes each day all around the school building. Many schools will also have a type of 'catch a student doing good policy.' Why not use all three of these things together; snap a photo of a student doing good with your camera phone, use Instagram to 'fancy' up the picture with a filter, then share it to the school website/blog to show off what students are doing.
Just like Angela Meiers and her Post It notes, an Administrator with a camera phone and Instagram has the potential to change the attitudes and lives of students.