With APT you can transmit and receive images acoustically. To do this each column of the selected gets transformed by a Fast Fourier Transform and outputed through iPhones speaker. On the receiving iOS-device the received audio is visualized by a spectrogram and the incoming images get visible. You can use this app for example to transmit images very easily over a phone or to put images in every kind of audio recording.

The pro-version has the additional features of choosing between two coding methods, choosing between linear and logarithmic frequency scale and the ability of sending the resulting audio as email. Also, the pro-version isn't ad-supported.