One option:

The idea is to use a tikzpicture and \nodes with the proper settings to place the elements at the desired locations; since internal calculations are involved, two runs are needed for the elements to appear at their final locations. Feel free to adjust the settings according to your needs.
The code:
\documentclass[11pt, landscape]{memoir}
%graphic packages
\usepackage{graphicx}
\usepackage{tikz}
\pagestyle{empty}
\parindent0pt
%fonts
\input Elzevier.fd
\newcommand*\initfamily{\usefont{U}{Elzevier}{xl}{n}}
\usepackage{calligra}
\usepackage[T1]{fontenc}
\usepackage{lipsum}
\begin{document}
\begin{tikzpicture}[
remember picture,
overlay,
mytext/.style={text width=\dimexpr0.5\paperwidth-20pt\relax,inner xsep=10pt}
]
\node[anchor=north west,inner sep=0]
at (current page.north west)
(image)
{\includegraphics[width=0.5\paperwidth,height=\paperheight]{mushrooms}};
\node[anchor=north,text=white,scale=2]
at ([yshift=-1cm]image.north)
{\initfamily{Hochzeit}};
\node[anchor=north west,text width=0.5\paperwidth,inner sep=0pt,minimum height=\paperheight]
at (current page.north)
(textbox)
{};
\node[anchor=north west,mytext]
at ([yshift=-2cm]textbox.north west)
(text1)
{\calligra{text and some other text}};
\node[anchor=north west,mytext]
at ([yshift=-5cm]textbox.north west)
(text2)
{\calligra{text and some other text}};
\node[anchor=south,mytext]
at ([yshift=3cm]textbox.south)
(text3)
{\calligra{text and some other text}};
\end{tikzpicture}
\end{document}
Update
Using the Elzevier package from the cfr-initials bundle, there's no need to input the font definition files:
\documentclass[11pt, landscape]{memoir}
%graphic packages
\usepackage{graphicx}
\usepackage{tikz}
\pagestyle{empty}
\parindent0pt
%fonts
\usepackage{calligra}
\usepackage{Elzevier}
\usepackage[T1]{fontenc}
\usepackage{lipsum}
\begin{document}
\begin{tikzpicture}[
remember picture,
overlay,
mytext/.style={text width=\dimexpr0.5\paperwidth-20pt\relax,inner xsep=10pt}
]
\node[anchor=north west,inner sep=0]
at (current page.north west)
(image)
{\includegraphics[width=0.5\paperwidth,height=\paperheight]{mushrooms}};
\node[anchor=north,text=white,scale=2]
at ([yshift=-1cm]image.north)
{\elz{Hochzeit}};
\node[anchor=north west,text width=0.5\paperwidth,inner sep=0pt,minimum height=\paperheight]
at (current page.north)
(textbox)
{};
\node[anchor=north west,mytext]
at ([yshift=-2cm]textbox.north west)
(text1)
{\calligra{text and some other text}};
\node[anchor=north west,mytext]
at ([yshift=-5cm]textbox.north west)
(text2)
{\calligra{text and some other text}};
\node[anchor=south,mytext]
at ([yshift=3cm]textbox.south)
(text3)
{\calligra{text and some other text}};
\end{tikzpicture}
\end{document}
The result:
