It is very hard to help you because you gave not much information and no minimal working example (MWE) , that at least shows how your backdrop will look like.
Here’s my new suggest.
Create the backdrop image using the standalone class:
% backdrop.tex
\documentclass[border=0cm]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\draw [blue] (0,0) grid (5,5);
\end{tikzpicture}
\end{document}
Give the image file backdrop.pdf that we now can include in the main document. For that we create a command \backdrop with three optional arguments:
\backdrop(coordiate)[node options][graphic options]
The first on takes a TikZ coordinate like 0,0, the second passes options to the node and the latter passes options to \includegraphics. Since all are optional you must give an empty second argument if you want to use only the third (see the example below). If you call \backdrop in text mode it will certainly ignore the first two arguments. Note: You can only change the node containing the image but not the image itself because it’s a PDF …
\documentclass{scrartcl}
\usepackage{tikz}
\usepackage{graphicx}
\usepackage{xparse}
% define a default style for the backdrop node
\tikzset{
backdrop node/.style={%
inner sep=0pt,
outer sep=0pt,
anchor=south west,
},
}
% define the layers
\pgfdeclarelayer{backdrop}
\pgfsetlayers{backdrop,main}
% defin the command to print the backdrop image
\NewDocumentCommand{\backdrop}{D(){0,0} O{} O{}}{%
\tikzifinpicture{% inside a TikZ-Picture
\begin{pgfonlayer}{backdrop}
\node at (#1) [backdrop node,#2]
{\includegraphics[#3]{backdrop}};
\end{pgfonlayer}
}{% in normal Text
\includegraphics[#3]{backdrop}
}%
}
\begin{document}
\section*{outside}
\backdrop
\section*{inside}
\begin{tikzpicture}
\backdrop
\fill [yellow] (1,1) rectangle (2,2);
\draw [red, ultra thick] (1,1) -- (4,4);
\backdrop(6,0)
\backdrop[rotate=30]
\backdrop[][width=1cm]
\backdrop(8.5,2.5)[anchor=center][width=3cm]
\end{tikzpicture}
\end{document}
Thats the result:

\backdropa little ? Nested tikzpictures are not recommended but it's possible if you take care but it's often possible to avoid this kind of situation ! – Alain Matthes Mar 25 '12 at 10:13\backdropis and we don't, it seems that the simplest thing would be simply to try it and see what happens. Then if something doesn't quite work, you can ask specifically about that and it might be easier for us to help. – Andrew Stacey Mar 25 '12 at 18:43