temporarily disable image with extension like '.ico' to make it the same iOS (just accept jpg, png and gif)

src/org/thoughtcrime/securesms/linkpreview/LinkPreviewRepository.java

@@ -147,6 +147,11 @@ public class LinkPreviewRepository implements InjectableType {
           imageUrl = Optional.absent();
         }
 
+        if (imageUrl.isPresent() && !LinkPreviewUtil.isVaildMimeType(imageUrl.get())) {
+          Log.i(TAG, "Image URL was invalid mime type. Skipping.");
+          imageUrl = Optional.absent();
+        }
+
         callback.onComplete(new Metadata(title, imageUrl));
       }
     });

src/org/thoughtcrime/securesms/linkpreview/LinkPreviewUtil.java

@@ -17,6 +17,7 @@ import org.thoughtcrime.securesms.util.DateUtils;
 import org.thoughtcrime.securesms.util.Util;
 import org.whispersystems.libsignal.util.guava.Optional;
 
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
@@ -96,6 +97,15 @@ public final class LinkPreviewUtil {
     }
   }
 
+  public static boolean isVaildMimeType(@NonNull String url) {
+    String[] vaildMimeType = {"jpg", "png", "gif", "jpeg"};
+    if (url.contains(".")) {
+      String extenstion = url.substring(url.lastIndexOf(".") + 1).toLowerCase();
+      return Arrays.asList(vaildMimeType).contains(extenstion);
+    }
+    return true;
+  }
+
   public static @NonNull OpenGraph parseOpenGraphFields(@Nullable String html) {
     return parseOpenGraphFields(html, text -> Html.fromHtml(text).toString());
   }