Something like this? Note that the images on the left are not all the same width because the images I used have different proportions. Provided yours have the same height:width ratio, they will match in width.
\documentclass[letterpaper]{article}
\usepackage[scale=1]{geometry}
\usepackage{tikz,calc}
\usetikzlibrary{positioning,calc}
\setlength\parindent{0pt}
\begin{document}
\begin{tikzpicture}
\fill [black] (current page.north east) rectangle (current page.south west);
\fill [gray] (current page.north west) rectangle ([xshift=50mm]current page.south west);
\node (person 0) [anchor=south, inner sep=0pt] at ([xshift=25mm,yshift=-10mm]current page.north west) {};
\foreach \i [count=\ino, remember=\ino as \j (initially 0)] in {example-image-9x16,example-image-golden-upright,example-image-9x16,example-image-golden-upright,example-image-9x16,example-image-golden-upright,example-image-9x16,example-image-golden-upright,example-image-9x16,example-image-golden-upright,example-image-9x16,example-image-golden-upright,example-image-9x16}
\node (person \ino) [anchor=north, inner sep=0pt] at (person \j.south) {\includegraphics[height=\paperheight/13-20mm/13] {\i} };
\node (title) [anchor=south, font=\Huge\bfseries, text=white] at ([xshift=25mm,yshift=-50mm]current page.north) {PROBABILITY THEORY};
\node (subtitle) [below=5mm of title.south, anchor=north, text=white, font=\LARGE\bfseries] {A Modern Comprehensive Course};
\path [line width=1pt, draw=white] ([yshift=-5mm]title.west |- subtitle.south) coordinate (a) -- ([yshift=-5mm]title.east |- subtitle.south) coordinate (b) ([xshift=2.5mm,yshift=-2.5mm]a) -- ([xshift=-2.5mm,yshift=-2.5mm]b) coordinate (c);
\node at ($(title.center |- c)!1/2!(current page.south -| title.center)$) {\includegraphics[height=.5\paperheight] {tiger}};
\end{tikzpicture}
\end{document}
Use
\usepackage{pdfpages}
...
\includepdf{<filename>}
if you wish to include it in your main document. (This seems odd since it presumably shouldn't be numbered, for example. But if you need it, you can do it.)
EDIT
I initially tried to use only images from the standard TeX distributions. Since nobody else is restricting themselves to that, I figure I might as well play, too. Here's a version which relies more on parameters to set the cover up. The basic code is the same. The only difference really is that some settings are no longer hard-coded. Probably not useful for a cover page, but perhaps handy in similar contexts where several pictures with the same structure might be used.
I'll keep the tiger, though. Standard or not....
\documentclass[letterpaper]{article}
\usepackage[scale=1]{geometry}
\usepackage{tikz,calc}
\usetikzlibrary{positioning,calc}
\setlength\parindent{0pt}
\newlength\coverscratch
\setlength\coverscratch{10mm}
\newlength\coverborder
\setlength\coverborder{30mm}
\tikzset{%
cover border left/.store in=\coverborderleft,
cover border right/.store in=\coverborderright,
cover border top/.store in=\coverbordertop,
cover border bottom/.store in=\coverborderbottom,
cover border images/.store in=\coverborderimages,
cover sample image/.code={%
\settowidth{\coverscratch}{\includegraphics[height=\paperheight/\coverborderimages-\coverbordertop/\coverborderimages-\coverborderbottom/\coverborderimages]{#1}}%
\setlength{\coverborder}{\coverborderleft+\coverborderright+\coverscratch}%
},
cover border image/.style={%
anchor=north,
inner sep=0pt,
node contents={\includegraphics[height=\paperheight/\coverborderimages-\coverbordertop/\coverborderimages-\coverborderbottom/\coverborderimages]{#1}},
},
cover title drop/.store in=\covertitledrop,
% make sure everything has a default
cover border left=10mm,
cover border right=10mm,
cover border top=2.5mm,
cover border bottom=2.5mm,
cover border images=13,
cover sample image={example-image-golden-upright},
cover title drop=50mm,
}
\begin{document}
\begin{tikzpicture}
[
cover border top=5mm,
cover border bottom=5mm,
cover border left=7.5mm,
cover border right=7.5mm,
cover sample image={people/Charles_Darwin},% best to set this last to ensure correct values are used
]
\fill [black] (current page.north east) rectangle (current page.south west);
\fill [gray] (current page.north west) rectangle ([xshift=\coverborder]current page.south west);
\node (person 0) [anchor=south, inner sep=0pt] at ([xshift=.5*\coverborder,yshift=-\coverbordertop]current page.north west) {};
\foreach \i [count=\ino, remember=\ino as \j (initially 0)] in {Albert_Einstein,Carl_Sagan,Charles_Darwin,Marie_Curie,Niels_Bohr,Nikola_Tesla,Richard_Feynman,Steven_Hawking,Stimpson_J,Albert_Einstein,Carl_Sagan,Charles_Darwin,Marie_Curie}
\node (person \ino) at (person \j.south) [cover border image={people/\i}];
\node (title) [anchor=south, font=\Huge\bfseries, text=white] at ([xshift=.5*\coverborder,yshift=-\covertitledrop]current page.north) {PROBABILITY THEORY};
\node (subtitle) [below=5mm of title.south, anchor=north, text=white, font=\LARGE\bfseries] {A Modern Comprehensive Course};
\path [line width=1pt, draw=white] ([yshift=-5mm]title.west |- subtitle.south) coordinate (a) -- ([yshift=-5mm]title.east |- subtitle.south) coordinate (b) ([xshift=2.5mm,yshift=-2.5mm]a) -- ([xshift=-2.5mm,yshift=-2.5mm]b) coordinate (c);
\node at ($(title.center |- c)!1/2!(current page.south -| title.center)$) {\includegraphics[height=.5\paperheight] {tiger}};
\end{tikzpicture}
\end{document}
