It is possible to use PGF/TikZ to draw a rectangle around the text area (or the whole page etc.).
I modified my answer to
Stretching a framebox over the whole page so it draws the rectangle around the full text area.
In my test it works well with the llncs class and others. You can place it in the footer then it is inserted on any page. Note that the rectangle goes to the baseline of the last line, i.e. the lower parts of the text go below it. That's normal and shouldn't be a problem in your case.
\documentclass{llncs}
\usepackage{tikz}
\usepackage{lipsum}
\usepackage{fancyhdr}
\pagestyle{fancy}
\renewcommand{\headrulewidth}{0pt}
\renewcommand{\footrulewidth}{0pt}
\rfoot{%
\begin{tikzpicture}[overlay,remember picture]
% Helper nodes
\path (current page.north west) ++(\hoffset, -\voffset)
node[anchor=north west, shape=rectangle, inner sep=0, minimum width=\paperwidth, minimum height=\paperheight]
(pagearea) {};
%
\path (pagearea.north west) ++(1in+\currentsidemargin,-1in-\topmargin-\headheight-\headsep)
node[anchor=north west, shape=rectangle, inner sep=0, minimum width=\textwidth, minimum height=\textheight]
(textarea) {};
%
% Framebox
\draw (textarea.north west) rectangle (textarea.south east);
%
\end{tikzpicture}%
}
\newcommand{\currentsidemargin}{%
\ifodd\value{page}%
\oddsidemargin%
\else%
\evensidemargin%
\fi%
}
\begin{document}
\lipsum[1-100]
\end{document}

pageframeseems to be deprecated (it is written for LaTeX 2.09). Don't you get an overfull hbox if your float extends into the margin? Note that you can use thedraftoption to visualize these. – Michael Ummels Mar 23 '11 at 10:27