Location of Account/ Login picture on Mac OS X 10.12 Sierra I used this solution - 

sudo dscl . -read /Users/$USER JPEGPhoto | tail -1 | xxd -r -p &gt; ~/Desktop/$USER.jpg


Is there any other better way to locate the filesystem storage location for this picture?
There is a terminal command that will print the path of the desktop picture on the picture itself. Using the terminal enter the following command:

defaults write com.apple.dock desktop-picture-show-debug-text -bool TRUE;killall Dock


Your desktop picture should now show the directory path to its location. When you get the location of the image you can turn this off by typing:

defaults delete com.apple.dock desktop-picture-show-debug-text;killall Dock