diff --git a/theme/background-en.jpg b/theme/background-en.jpg
new file mode 100644
index 0000000000000000000000000000000000000000..c7748212a010f8420c0970a8feb47d33f4b52106
Binary files /dev/null and b/theme/background-en.jpg differ
diff --git a/theme/background-en.png b/theme/background-en.png
deleted file mode 100644
index 5a1899ebbcecf8de29662766c401603f09954eba..0000000000000000000000000000000000000000
Binary files a/theme/background-en.png and /dev/null differ
diff --git a/theme/background.jpg b/theme/background.jpg
new file mode 100644
index 0000000000000000000000000000000000000000..266cd7200f9e4757fdefa4227f407e59ff6bf3a5
Binary files /dev/null and b/theme/background.jpg differ
diff --git a/theme/background.png b/theme/background.png
deleted file mode 100644
index 75a531501c14f740876f565a1a6bede2fbc802ea..0000000000000000000000000000000000000000
Binary files a/theme/background.png and /dev/null differ
diff --git a/theme/beamerinnerthemeost.sty b/theme/beamerinnerthemeost.sty
index e196825c8b28bfb0d4ada49f9f0445e455678b22..16da9545ae37d004cfe4f7b672e11915648a9521 100644
--- a/theme/beamerinnerthemeost.sty
+++ b/theme/beamerinnerthemeost.sty
@@ -5,7 +5,7 @@
     \begin{tikzpicture}
         \useasboundingbox (0,0) rectangle(\the\paperwidth,\the\paperheight);
         \node[opacity=1,inner sep=0pt] at (current page.center){
-            \includegraphics [height=\paperheight]{\iflanguage{english}{background-en.png}{background.png}}};
+	    \includegraphics [height=\paperheight]{\iflanguage{english}{background-en.jpg}{background.jpg}}};
     \end{tikzpicture}
   \fi
 }