I’m running latex under Texmaker version 3.0.2 on Ubuntu version 10.04.
I wanted to insert into my latex file a simple picture named “classes.png” as follows:

\begin{figure}
\centering
\includegraphics[scale=1, width=14cm]{classes.png}
\caption{Diagramme de classes}
\end{figure}

I got the following error:

! LaTeX Error: Cannot determine size of graphic in classes.png (no BoundingBox).

I did everything to fix this trouble starting from changing the extension of my picture to totally convert to an eps and pdf files but in vain. So, I went reading through details about latex packages and finally fixed the trouble as follows:

1-I went to Options -> Configure Texmaker
2-I pressed on the Quick Build button
3-I switched the Quick Build command to PdfLatex + View PDF
4-I pressed on the Editor button
5-I scrolled through the Editor Font Encoding and I chosed UTF-8
6-I pressed OK to validated my changes.
7-I came back to compile my latex file: it works !

Any question ? You’re welcome !