How to watch a periodically shot image on other PC/Smartphone via Internet (no local WIFI)?
Another approach:

The free app IP webcam is a video streaming tool primarily, but there's also an option to fetch only a photo. It brings a webserver where /photo.png is a continuously updated resource. Since it gets refreshed each time you request it via a browser, you don't have to care about taking a picture every X minutes.

You then can use port forwarding on the router to access the phone's webserver from www.

Ip webcam also features authentication with username/password, but I don't know how secure it is.