When an app wants to take a photo it will open a dialog where you can select the camera app to use to take the photo. There it's possible to select the Gallery Camera. The Gallery Camera app opens the library instead of the camera where a picture can be selected. The selected picture is then returned to the initial app as the photo taken.
According to the antivirus report, this application doesn't contain viruses or any kind of malware. ZInformatik is the developer of the app that refers to the Tools category. According to the latest data, Gallery Camera is rated 3.7 on Google Play.
This application has been downloaded and set up by over 100K users and the most recent update is dated Jul 10, 2015. Download the latest .apk file of Gallery Camera 1.0 for free and have a look at users' reviews on Droid Informer. You will need 1 MB of free disk space to set up the app which is compatible with Android 2.2 and above.