The app, called MindRDR, works through a second headset that the user wears alongside Google Glass, and communicates with the wearable device through Bluetooth.
It was created by London-based start-up This Place, which came up with the idea after using Glass, and finding that it could be more hands-free.
The headset, called the Neurosky EEG biosensor, uses a sensor that sits on your forehead and measures brainwaves. Concentrating triggers a higher brainwave reading, and this tells the app to take a picture, and then post it to Twitter.
Chloe Kirton, the company's creative director, said: "We started off by getting hold of Google Glass, which was really exciting for us - we really respect them and getting hold of one of their new products was really exciting.
"But when we started to use it we started to encounter what maybe you could call a usability issue; which is when you're swiping around looking for photos your arm can get a bit tired and we found ourselves holding our arms up and using the device, and we affectionately called this Glass elbow.
"So we wanted to task ourselves with finding a better way of using it, and not everyone has the high level of dexterity that is needed. The idea of mind control came up and we thought lets run with that and see where it can go. "