/data/system/users/0/photo.png is the picture you're looking for. But, you cannot get that pic or even visit its parent directory without elevated privileges. adb shell isn't enough to get it.
There is a catch here. In my Paranoid ROM (AOSP) I found that the owner is supposed to create a contact (about me) for himself. Any image used in that contact is directly user by the system as the image of the user, and hence, gets copied to that said location. This isn't the case in CM12 though.
The images provided to contacts are saved at the location
/data/data/com.android.providers.contacts/files/photos. Your profile image is saved in
Both location are inaccessible by ADB and an ordinary user. Now that I've given you ample stuff to search and research, it is up to you to choose a path: 1) root and get the stuff easily, 2) find an app that can copy the profile or contacts images in a standard format from which you can retrieve your profile image.