Tikzpicture Unable to Genrate png in Org

I was trying to embed tikzpicture code in my org files. But fount that whenever I want to output the latex source code written to generate a picture, I was only able to do it when the :file option is set to svg. It will give not authorized error for png files.

For example, I have the following code blocks in my org file:

#+name: 2.24-list-tree
#+header: :results value file
#+header: :file images/2.24-tree.png 
#+header: :imagemagick yes :headers '("\\usepackage{tikz}") 
#+header: :fit yes :iminoptions -density 600 :imoutoptions -geometry 400
#+begin_src latex :file ./images/2.24-tree.png
  \begin{tikzpicture}
    \node {root}
      child {node {1}}
      child {node {(2 (3 4))}
        child {node {2}}
        child {node {(3 4)}
          child {node {3}}
          child {node {4}}
        }
      };
  \end{tikzpicture}
#+end_src

and it never generates the file. Later I found that the issue is with the debian version of the package imagemagick. In order to re-enable us to generate png files, do the following:

1. Switch to root user
2. Edit file /etc/ImageMagic-6/policy.xml
3. Replace <policy domain="coder" rights="none" pattern="PDF" /> with

1. Save it.

Now we should be able to generate png files just fine.

I found the solution here.