Try this code. (I understood that the figure goes at the top of the page.)
Change the font size of the word chapter and of the chapter number using \fontsize{<size>}{<skip>}
. Modify their position using xshift
and yshift
Also \titlespacing*{\chapter}{<space left>}{<space above>}{<space below>}
for the chapter title.

\documentclass[a4paper, twoside, 12pt, final]{report}
\usepackage[utf8]{inputenc}
% custom section headers
\RequirePackage{titlesec}
\usepackage{tikz}
\usetikzlibrary{positioning} % added <<<<<<<<<<<<<
\usepackage{anyfontsize} % added to change fonts with pdflatex <<<<<<<<<<<<<
\usepackage{lipsum}
\RequirePackage{xcolor}
\definecolor{RoyalRed}{RGB}{157,16, 45}
\newcommand{\ChapLabel}{\fontsize{36pt}{44pt}\selectfont \color{RoyalRed} \MakeUppercase{\chaptertitlename}}% set the word Chapter
\newcommand{\ChapNum}{\fontsize{120pt}{144pt}\selectfont \color{RoyalRed} \thechapter}% set the chapter number
\newcommand{\MakeChap}{\ChapLabel\enspace\ChapNum}
\titleformat{\chapter}[display]
{ \normalsize \LARGE \color{black}} {%
\begin{tikzpicture}[remember picture,overlay]
\node(blue)[opacity=0.9,inner sep=0pt,anchor=north] at (current page.north){\includegraphics[width=\paperwidth,height=10cm]{blue.jpg}};
\node [below= of blue.south east, anchor=base east, xshift=-\marginparsep, yshift=-1ex] {\MakeChap};
\end{tikzpicture}}
{10pt}{\bfseries\huge}
\titlespacing*{\chapter}{0pt}{170pt}{20pt} % changed <<<<<<<<<<<<<<
\begin{document}
\chapter{Introduction}
\lipsum[2-8]
\end{document}
UPDATE after follow up question. (Figure at the bottom and subtitles.)
Use \Schapter{<chapter title>}{<subtitle>}
to add a subtitle.

% !TeX TS-program = pdflatex
\documentclass[a4paper, twoside, 12pt, final]{report}
\usepackage[utf8]{inputenc}
% custom section headers
\RequirePackage{titlesec}
\usepackage{tikz}
\usetikzlibrary{positioning} % added <<<<<<<<<<<<<
\usepackage{anyfontsize} % added for change fonts with pdflatex <<<<<<<<<<<<<
\usepackage{fancyhdr} % added <<<<<<<<<<<<<
\fancypagestyle{plain}{% style plain >>> empty for chapter page
\fancyhf{}
\renewcommand{\headrulewidth}{0pt}
\renewcommand{\footrulewidth}{0pt}
}
\usepackage{lipsum}
\RequirePackage{xcolor}
\definecolor{RoyalRed}{RGB}{157,16, 45}
\newcommand{\ChapLabel}{\fontsize{30pt}{36pt}\selectfont \color{RoyalRed}\sffamily \MakeUppercase{\chaptertitlename}}% set the word Chapter
\newcommand{\ChapNum}{\fontsize{120pt}{144pt}\selectfont \color{RoyalRed}\sffamily \thechapter}% set the chapter number
\newcommand{\MakeChap}{\vspace*{10cm}\ChapLabel\enspace\ChapNum}
\titleformat{\chapter}[display]
{ \normalsize \LARGE \color{black}} {%
\enlargethispage{-7cm}
\begin{figure}[b]%
\begin{tikzpicture}[remember picture,overlay]
\node(blue)[opacity=0.9,inner sep=0pt,anchor=south] at (current page.south){\includegraphics[width=\paperwidth,height=10cm]{blue.jpg}};
\node (chap) [above= of blue.north east, anchor=south east, xshift=-\marginparsep-\marginparwidth-30pt, yshift=-4ex] {\ChapLabel};
\node [right= of chap.south east, anchor=base west, xshift= -\marginparwidth+12ex, yshift=-6ex] {\ChapNum};
\end{tikzpicture}
\end{figure}}
{10pt}{\bfseries\huge}
\titlespacing*{\chapter}{0pt}{-30pt}{20pt} % changed <<<<<<<<<<<<<<
\newcommand{\Schapter}[2]{\chapter[#1]{#1\\[1ex] \parbox{0.7\linewidth}{\large#2}}}% add subtitles <<<<<<<<<<<<<<<
\begin{document}
\Schapter{Introduction}{Nam lacus libero, pretium at, lobortis vitae, ultricies et, tellus}
\lipsum[2-8]
\end{document}