ProvidesPackage{titlepageFormat}[2017-10-17 v0.1]
renewcommand*{maketitle}{%
begin{titlepage}
Header\
vspace{5cm}
centering
{large Title\}
vspace{3cm}
raggedright
vfill
Author\
vspace{1.5cm}
Footer\
vspace{1.5cm}
end{titlepage}
}
endinput

begin{textblock*}{100mm}(50mm,75mm) % {〈hsize〉}[〈ho〉,〈vo〉](〈hpos〉,〈vpos〉)
  includegraphics{example-image-a}% a full-page picture?
end{textblock*}%

documentclass{scrreprt}

usepackage[absolute]{textpos} % https://www.ctan.org/pkg/textpos
usepackage{graphicx}

begin{document}

begin{titlepage}
begin{textblock*}{100mm}(50mm,75mm) % {〈hsize〉}[〈ho〉,〈vo〉](〈hpos〉,〈vpos〉)
  includegraphics{example-image-a}% a full-page picture?
end{textblock*}%
Header\
vspace{5cm}
centering
{large Title\}
vspace{3cm}
raggedright
vfill
Author\
vspace{1.5cm}
Footer\
vspace{1.5cm}
end{titlepage}

end{document}