Add citation for images

bibliography.bib

@@ -51,6 +51,14 @@ year={2007}
   urldate = {2022-09-28},
 }
 
+@unpublished{spg,
+  Author = {Skornia, Christoph},
+  Institution = {OTH Regensburg},
+  Howpublished = {University Lecture},
+  Year = {2021},
+  Title = {Secure Programming --- Input Validation},
+}
+
 @misc{directoryStructure,
   title = {Classic SysAdmin: The Linux Filesystem Explained},
   Institution = {The Linux Foundation},

bof.tex

@@ -121,12 +121,20 @@
 \section{Stack Layout, Execution Flow}
 \begin{frame}
   \frametitle{Stack Layout}
-\includegraphics[width=.30\textwidth]{stack.png}
+  \begin{figure}
+    \centering
+    \includegraphics[width=.25\textwidth]{stack.png}
+    \caption{Stack Layout~\cite{spg}}
+  \end{figure}
 \end{frame}
 
 \begin{frame}
   \frametitle{Stack Layout}
+  \begin{figure}
+    \centering
     \includegraphics[width=.60\textwidth]{stack_overflow.png}
+    \caption{Buffer Overflow~\cite{spg}}
+  \end{figure}
 \end{frame}
 
 \begin{frame}
@@ -153,7 +161,6 @@
         \item \url{https://www.exploit-db.com/shellcodes}
       \end{itemize}
   \end{itemize}
-% \frametitle{Exkurs: Shellcode}
 \end{frame}
 
 \section{Exploitation}