diff --git a/docs/index.html b/docs/index.html
index 34ea545..8105e82 100755
--- a/docs/index.html
+++ b/docs/index.html
@@ -35,22 +35,22 @@
       content="Rui, Yifan, Kai, Yikuan, Sebin, Weiye, Changliu. SPARK at ICL." />
     <meta property="og:url" content="https://intelligent-control-lab.github.io/spark/" />
     <meta property="og:image"
-      content="https://intelligent-control-lab.github.io/spark/static/images/preview.jpg" />
+      content="https://intelligent-control-lab.github.io/spark/static/images/preview.png" />
     <meta property="og:image:secure"
-      content="https://intelligent-control-lab.github.io/spark/static/images/preview.jpg" />
+      content="https://intelligent-control-lab.github.io/spark/static/images/preview.png" />
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       content="https://www.youtube.com/embed/vIzeQ31YbCM?rel=0&showinfo=0&modestbranding=1" />
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     <meta property="article:publisher" content="https://intelligent-control-lab.github.io/spark/" />
-    <meta name="twitter:card" content="https://intelligent-control-lab.github.io/spark/static/images/preview.jpg" />
+    <meta name="twitter:card" content="https://intelligent-control-lab.github.io/spark/static/images/preview.png" />
     <meta name="twitter:title" content="Safe Humanoid" />
     <meta name="twitter:description"
       content="Rui, Yifan, Kai, Yikuan, Sebin, Weiye, Changliu. SPARK at ICL." />
     <meta name="twitter:url" content="https://intelligent-control-lab.github.io/spark/" />
     <meta name="twitter:image"
-      content="https://intelligent-control-lab.github.io/spark/static/images/preview.jpg" />
+      content="https://intelligent-control-lab.github.io/spark/static/images/preview.png" />
     <!-- <meta name="twitter:label1" content="Written by" />
   <meta name="twitter:data1" content="Deepak Pathak" /> -->
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@@ -62,7 +62,7 @@
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     <meta name="twitter:card" content="player" />
     <meta name="twitter:image"
-      content="https://intelligent-control-lab.github.io/spark/static/images/preview.jpg" />
+      content="https://intelligent-control-lab.github.io/spark/static/images/preview.png" />
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