inclugraphics[scale=TRYING TO GUESS THE NUMBER FOR PAGE WIDTH]{...}

begin{center}
  makebox[textwidth]{includegraphics[width=paperwidth]{...}}
end{center}

noindentmakebox[textwidth]{includegraphics[width=paperwidth]{...}}

documentclass{article}
usepackage{graphicx,changepage}

newcommand{adjustimg}{% Horizontal adjustment of image
  checkoddpage%
  ifoddpagehspace*{dimexprevensidemargin-oddsidemargin}elsehspace*{-dimexprevensidemargin-oddsidemargin}fi%
}
newcommand{centerimg}[2][width=textwidth]{% Center an image
  makebox[textwidth]{adjustimgincludegraphics[#1]{#2}}%
}

begin{document}
mbox{} par
noindentcenterimg[width=paperwidth,height=200pt]{tiger}

newpage

mbox{} par
noindentcenterimg[width=paperwidth,height=200pt]{tiger}
end{document}

begin{center}
begin{figure}[ht]
centering
     includegraphics[width=1.0textwidth]{Normal_Case_1_req_1_response}
      caption{Normal Case: 1 Request & 1 Response.}
       label{normal_case}
end{figure}
end{center}

usepackage{pdfpages}
...
includepdf{image.png}