For iOS users iSelfie is a free app that makes easy for selfies to take photos by pairing two of iDevices via Bluetooth or Wi-Fi. It means one device will remotely control the camera of other device and let you allow to take photos remotely.
On both of your iDevices you have to install iSelfie app, and then create a connection between devices through bluetooth or wi-fi network to make one host and the other remote to take photos.
If you have enabled Apple Photo Stream on your both iDevices, then the photos taken by iSelfie will be saved on both, otherwise obviously just on the host device, which camera you are using to take photos.
iSelfie is compatible for iPhone, iPod touch and iPad running over iOS 5 or later. Its file size is 1.4 MB and the app is available free for download via App Store.