Decreased the suggested minimum DPI to 300.

example/mu/example.dtx

@@ -567,10 +567,14 @@ proofs.
   \begin{center}
     %% PNG and JPG images can be inserted into the document as well,
     %% but their resolution needs to be adequate. The minimum is
-    %% about 250 pixels per 1 centimeter. That means that a JPG or
-    %% PNG image typeset at 40 × 40 mm should be 1000 × 1000 px
-    %% large at minimum.
-    \includegraphics[width=40mm]{fithesis/logo/mu/fithesis-base.pdf}
+    %% about 100 pixels per 1 centimeter or 300 pixels per 1 inch.
+    %% That means that a JPG or PNG image typeset at 4 × 4 cm should
+    %% be 400 × 400 px large at the bare minimum.
+    %%
+    %% The optimum is about 250 pixels per 1 centimeter or 600
+    %% pixels per 1 inch. That means that a JPG or PNG image typeset
+    %% at 4 × 4 cm should be 1000 × 1000 px large or larger.
+    \includegraphics[width=4cm]{fithesis/logo/mu/fithesis-base.pdf}
   \end{center}
   \caption{The logo of the Masaryk University at 40\,mm}
   \label{fig:mulogo1}