Tikz scopes with coordinates relative to a node

tikzonnode.tex

% This file adds two environments for TkiZ.
%
% The first, tikzonnode, simply changes the coordinate system so that (0,0) is
% at the south west anchor of the given node and (1,1) is at the north east 
% anchor.
%
% The second environment, tikzonimage, displays the given image file (the first
% optional argument is passed to \includegraphics) and creates a tikzpicture on
% top of it with coordinates relative to the image corners.
%
% Both environments accept an optional argument with TikZ options.
\documentclass{article}
\usepackage{tikz}

\makeatletter
\def\tikzonnode#1{%
    \pgfutil@ifnextchar[{\tikzonnode@opt#1}{\tikzonnode@opt#1[]}%
}
\def\endtikzonnode{%
    \end{scope}%
}
\def\tikzonnode@opt#1[#2]{%
    \pgfpointanchor{#1}{south west}%
    \pgfgetlastxy\tse@tikz@shift@x\tse@tikz@shift@y
    \begin{scope}[
            shift={(\tse@tikz@shift@x,\tse@tikz@shift@y)},
            x={(#1.south east)},
            y={(#1.north west)},
            #2]%
}

\def\tikzonimage{%
    \pgfutil@ifnextchar[{\tikzonimage@opt}{\tikzonimage@opt[]}%
}
\def\tikzonimage@opt[#1]#2{%
    \begin{tikzpicture}
        \node[inner sep=0] (image) {\includegraphics[#1]{#2}};
        \begin{tikzonnode}{image}%
}
\def\endtikzonimage{%
        \end{tikzonnode}
    \end{tikzpicture}%
}
\makeatother

\begin{document}
\begin{tikzonimage}[width=0.3\textwidth]{some_image.jpg}[color=red]
    \node at (0,0) {test};
\end{tikzonimage}

\begin{tikzpicture}
    \node (A) [text width=2cm] {abc abc abc abc abc abc abc abc abc};
    \begin{tikzonnode}{A}[color=red]
        \node at (0,0) {test};
    \end{tikzonnode}
\end{tikzpicture}
\end{document}