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\begin{figure}[ht]
\centering
\includegraphics[width=1.0\textwidth]{Normal_Case_1_req_1_response}
\caption{Normal Case: 1 Request \& 1 Response.}
\label{normal_case}
\end{figure}
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\documentclass{report}
\usepackage[english]{babel}
\usepackage{graphicx}
\begin{document}
\includegraphics[height=3cm]{example-image-b}
\includegraphics[width=5cm]{example-image-b}
\includegraphics[height=3cm, width=3cm]{example-image-b}
\includegraphics[height=3cm, width=6cm]{example-image-b}
\includegraphics[keepaspectratio,height=3cm, width=6cm]{example-image-b}
\end{document}