Android 4.3 Camera App from Google Edition Galaxy S4 Leaked
Aside from some UI changes, the 4.3 Camera app seems to have the same feature set (including Photosphere) as the 4.2 Camera app. The leaked 4.3 Camera app is easy to install, as it can be installed as an APK. It also seems to be largely compatible with Galaxy Nexus, S2, S3, S4, Note, and Note II devices running on 4.1.x/4.2 TouchWiz and AOSP-based ROMs.
You can grab the leaked camera app from the XDA Developer Forums.
Phandroid -Android 4.3 for the Google Play edition Galaxy S4 leaked, new camera app available for download
xda developers – [App]Samsung Galaxy S4 Google Edition Camera