\documentclass[a4paper,12pt,oneside,openright,titlepage]{book}
\usepackage[english]{babel}
\usepackage{newlfont}
\textwidth=450pt\oddsidemargin=0pt
\usepackage[T1]{fontenc}
\usepackage{indentfirst}
\usepackage{fancyhdr}
\usepackage{showkeys}
\usepackage[dvips]{graphicx}
\usepackage{mathdots}
\usepackage[labelfont=bf]{caption}
\usepackage{bm} % per fare le lettere greche minuscole in grassetto
\usepackage{blkarray}
\BAnewcolumntype{C}{>{$}c<{$}}
\usepackage{amssymb}
\usepackage{amsmath, amsthm, amssymb}
\usepackage{latexsym}
\usepackage{amsthm}
\usepackage{eucal}
\usepackage{guit}
\usepackage{multirow}
\usepackage{longtable}
\usepackage{float}
\usepackage{colortbl,booktabs,caption,float}
\usepackage{subfig}
\usepackage{yfonts}
\usepackage{epsf}
\usepackage{epstopdf}
\usepackage{eso-pic,graphicx}
\makeatletter
\newcommand\BackgroundPicture[2]{
\setlength{\unitlength}{1pt}
\put(0,\strip@pt\paperheight){
\parbox[t][\paperheight]{\paperwidth}{
\vfill
\centering\includegraphics[width=0.9\paperwidth]{#1}
\vfill
}
}
}
\makeatother
\begin{document}
...
\end{document}