Did you know that whenever you take a (digital) photo your camera usually saves (in the photo) a bunch of additional private (meta-)data? Most of this can be usually found in the properties of the respective file. An example is show bellow:
This is called EXIF (i.e., Exchangeable image file format; also see http://en.wikipedia.org/wiki/Exchangeable_image_file_format), and can include the exact camera model, date/time information, and in some cases (depending on the camera, or the smartphone in this case) even GPS data (i.e., the exact place of the photo taken). It is important to remember this whenever we post a photo anywhere in the Internet (whether it’s facebook -well it’s your choice not to do that ;), or a photo from a demonstration in a leftist/anarchist site).
So, how do we remove this?
Windows:
There are plenty of ways including doing it manually. For instance in a Windows machine this can be done by clicking in the properties of the image (also see http://www.makeuseof.com/tag/3-ways-to-remove-exif-metadata-from-photos-and-why-you-might-want-to/) and manually removing everything you can. However, as windows won’t really delete anything, you can also try the plethora of free available tools (just google for “remove exif data”, tools like Easy Exif Delete, etc. should do the trick; yet you should always manually check the properties of the photo afterwards to be sure.
Linux:
In a linux/debian/ubuntu system this can be easily done through many different tools (e.g., libimage-exiftool-perl or jhead ; sudo apt-get install libimage-exiftool-perl and/or sudo apt-get install jhead respectively).
Finally an alternative way (if you are really picky) is to make a screenshot of the actual photo, save/edit it as you wish, and then (just to be sure) run again an exif removal tool.