Index: apps/plugins/imageviewer/imageviewer.c
===================================================================
--- apps/plugins/imageviewer/imageviewer.c	(リビジョン 28900)
+++ apps/plugins/imageviewer/imageviewer.c	(作業コピー)
@@ -148,8 +148,9 @@
 
     for (i = 0; i < tree->filesindir && buf_size > sizeof(char**); i++)
     {
-        if (!(dircache[i].attr & ATTR_DIRECTORY)
-            && get_image_type(dircache[i].name) != IMAGE_UNKNOWN)
+        /* add all files (i.e. exclude all directory). will be filtered out
+           when loading. */
+        if (!(dircache[i].attr & ATTR_DIRECTORY))
         {
             file_pt[entries] = dircache[i].name;
             /* Set Selected File. */
@@ -721,7 +722,13 @@
 
     rb->lcd_clear_display();
 
-    status = get_image_type(filename);
+    /* suppress warning while running slideshow */
+    status = get_image_type(filename, !iv_api.running_slideshow);
+    if (status == IMAGE_UNKNOWN) {
+        /* file isn't supported image file, skip this. */
+        file_pt[curfile] = NULL;
+        return change_filename(direction);
+    }
     if (image_type != status) /* type of image is changed, load decoder. */
     {
         struct loader_info loader_info = {
@@ -893,7 +900,7 @@
     if(!parameter) return PLUGIN_ERROR;
 
     rb->strcpy(np_file, parameter);
-    if (get_image_type(np_file) == IMAGE_UNKNOWN)
+    if (get_image_type(np_file, false) == IMAGE_UNKNOWN)
     {
         rb->splash(HZ*2, "Unsupported file");
         return PLUGIN_ERROR;
Index: apps/plugins/imageviewer/image_decoder.c
===================================================================
--- apps/plugins/imageviewer/image_decoder.c	(リビジョン 28900)
+++ apps/plugins/imageviewer/image_decoder.c	(作業コピー)
@@ -29,8 +29,14 @@
     "png",
 };
 
-/* check file type by extention */
-enum image_type get_image_type(const char *name)
+/* check file type by magic number or file extension
+ *
+ * if the file contains magic number, use it to determine image type.
+ * otherwise use file extension to determine image type.
+ * if the file contains magic number and file extension is not correct,
+ * error message will be shown and user will know something is wrong.
+ */
+enum image_type get_image_type(const char *name, bool warn)
 {
     static const struct {
         char *ext;
@@ -42,18 +48,61 @@
         { ".jpeg",  IMAGE_JPEG },
         { ".png",   IMAGE_PNG  },
     };
+    static const struct {
+        char *magic;    /* magic number */
+        int length;     /* length of the magic number */
+        enum image_type type;
+    } magic_list[] = {
+        { "\x42\x4d", 2, IMAGE_BMP  },
+        { "\xff\xd8\xff\xe0", 4, IMAGE_JPEG },
+        { "\x89\x50\x4e\x47\x0d\x0a\x1a\x0a", 8, IMAGE_PNG },
+    };
 
+    enum image_type type = IMAGE_UNKNOWN;
     const char *ext = rb->strrchr(name, '.');
-    int i;
-    if (!ext)
-        return IMAGE_UNKNOWN;
+    int i, fd;
+    char buf[12];
 
-    for (i = 0; i < (int)ARRAYLEN(ext_list); i++)
+    /* check file extention */
+    if (ext)
     {
-        if (!rb->strcasecmp(ext, ext_list[i].ext))
-            return ext_list[i].type;
+        for (i = 0; i < (int)ARRAYLEN(ext_list); i++)
+        {
+            if (!rb->strcasecmp(ext, ext_list[i].ext))
+            {
+                type = ext_list[i].type;
+                break;
+            }
+        }
     }
-    return IMAGE_UNKNOWN;
+    else
+    {
+        ext = "???";
+    }
+
+    /* check magic value in the file */
+    fd = rb->open(name, O_RDONLY);
+    if (fd >= 0)
+    {
+        rb->memset(buf, 0, sizeof buf);
+        rb->read(fd, buf, sizeof buf);
+        rb->close(fd);
+        for (i = 0; i < (int)ARRAYLEN(magic_list); i++)
+        {
+            if (!rb->memcmp(buf, magic_list[i].magic, magic_list[i].length))
+            {
+                if (warn && type != magic_list[i].type)
+                {
+                    /* file extension is wrong. */
+                    rb->splashf(HZ*1,
+                        "File extension might not be correct: %s", ext);
+                }
+                type = magic_list[i].type;
+                break;
+            }
+        }
+    }
+    return type;
 }
 
 static void *decoder_handle = NULL;
Index: apps/plugins/imageviewer/image_decoder.h
===================================================================
--- apps/plugins/imageviewer/image_decoder.h	(リビジョン 28900)
+++ apps/plugins/imageviewer/image_decoder.h	(作業コピー)
@@ -39,8 +39,11 @@
     size_t size;
 };
 
-enum image_type get_image_type(const char *name);
+/* check file type by magic number or file extension */
+enum image_type get_image_type(const char *name, bool warn);
+/* load image decoder */
 const struct image_decoder *load_decoder(struct loader_info *loader_info);
+/* release the loaded decoder */
 void release_decoder(void);
 
 #endif /* _IMAGE_DECODER_H */