Cannot determine size of graphic

The DVI producing latex doesn't support reading the size of PNG, JPG or PDF images. You need to use pdflatex for this. Actually latex is pdflatex in DVI mode in modern distributions, but it can read the sizes only in PDF mode for some reason. You are however able to state the natural size of the images using natwidth and natheight which will make latex compile without error. The produced DVI file will only link to the PDF and the DVI-to-PDF converter will need to include it in the final PDF. AFAIK dvpdf doesn't support this but dvipdfm does.

\documentclass{article}

\usepackage{graphicx}

\begin{document}
\begin{figure}
    \centering
    \includegraphics[width=0.8\textwidth,natwidth=610,natheight=642]{tiger.pdf}
\end{figure}
\end{document}

Compile with either

pdflatex <file base>

or

latex <file base>
dvipdfm <file base>

A non-Latex solution

A very fast solution is to convert the png file into eps format. It can be done easily using graphic software, for instance Inkscape.

So, you only need to open the file in Inkscape and then SaveAs and select eps format.

Now change the extension in the tex file from

\includegraphics[width=0.8\textwidth]{tiger.png}

to

\includegraphics[width=0.8\textwidth]{tiger.eps}

Fix the file name

I got this error with a pdf file which contained dots in the filename. Removing the dots (except the .pdf, of course) fixed the issue.

Fix file type detection

The LaTeX graphics/graphicx package uses the first dot to find the extension. Simply adding \usepackage{graphicx} \usepackage{grffile} fixed the issue without changing file names. Package grffile changes the algorithm to check for known extensions (option multidot, enabled by default).