\documentclass[a4paper,ngerman,landscape]{scrartcl}

\usepackage{hyperref}
\usepackage{graphicx}
\usepackage{lmodern}

\usepackage{geometry}
\geometry{tmargin=1.5cm,bmargin=0.5cm,lmargin=2.5cm,rmargin=2.5cm}

\pagestyle{empty}

\newcommand{\comic}[3]{\begin{center}
  \includegraphics[scale=#3]{#1} \\[2em]

  Quelle: \url{#2}
\end{center}\newpage}

\newcommand{\comicQ}[2]{\begin{center}
  \includegraphics[scale=#2]{#1}
\end{center}\newpage}

\begin{document}

\comic{purity.png}{http://xkcd.com/435}{0.8}
\comic{three-logicians.png}{http://spikedmath.com/445.html}{1.4}
\comic{540-adventures-of-martin.png}{http://http://spikedmath.com/540.html}{1.4}
\comic{this_is_what_my_room_looks_like_when_i_draw}{http://abstrusegoose.com/287}{0.4}
\comic{542-science-vs-math}{http://spikedmath.com/542.html}{1.4}
\comic{353-fortune-teller-1}{http://spikedmath.com/353.html}{1.4}
\comic{355-fortune-teller-3}{http://spikedmath.com/355.html}{1.4}
\comic{labyrinth_puzzle}{http://xkcd.com/246}{2.7}
\comic{nerd_sniping}{http://xkcd.com/356}{0.8}
\comic{correlation}{http://xkcd.com/552}{1.6}
\comic{homer}{http://spikedmath.com/396.html}{2.4}
\comic{547-the-perfect-score}{http://spikedmath.com/547.html}{1.3}
\comic{346-cookies}{http://spikedmath.com/346.html}{1.3}
\comicQ{boromir-gauss}{1.3}

\end{document}
