LaTeX: How to set the pdf dpi when using images

I'm writing my thesis in LaTeX and I have troubles with the image imports.

I want to get my thesis as a PDF, which imports some JPEG images of charts and other开发者_如何学C things. I'd like to have a higher resolution; by default MikTeX settings I have my image resized to a crappy resolution.

I'm using MikTeX, Adobe Reader 9.4, Win7 32.

How can I raise the resolution of the PDF produced from my LaTeX sources?

Is there any other way to insert a pick without losing resolution?

I know about vectorial formats, but I have only BMP or JPG to insert in my thesis.

A part of the code is this: (the first 2 rows doesn't work =/)

\pdfpxdimen=2in    
\divide\pdfpxdimen by 300

\documentclass[12pt, a4paper]{report}

\usepackage[italian]{babel}    
\usepackage[T1]{fontenc}    
\usepackage{graphicx}

\begin{document}

\include{Frontespizio}

\newpage

\include{Ringraziamenti}

\tableofcontents 

\newpage

\include{Introduzione}

\pagenumbering{roman}


\pagenumbering{arabic}

\pagestyle{fancy}

\lhead{} \chead{} \rhead{\scriptsize \leftmark} \lfoot{}

\cfoot{\thepage} \rfoot{}

\renewcommand{\headrulewidth}{0.1pt}

\include{Capitolo1}

\newpage

\end{document}

And the Image calling is:

\begin{figure*}[h]    
    \centering    
        \includegraphics[width=\textwidth]{UseCase.png}    
    \label{fig: Use Cases}    
\end{figure*}

First of all, i suggest you to use .png images.

If you still want to change dpi you may insert this code on .tex preamble:

\pdfpxdimen=1in

\divide\pdfpxdimen by 96

(for 96dpi)