diff --git a/src/common.h b/src/common.h
index 5c8e0d1..2544be5 100644
--- a/src/common.h
+++ b/src/common.h
@@ -45,4 +45,5 @@ struct image *filter_trick(struct image *img);
 struct image *filter_smooth(struct image *img);
 struct image *filter_median(struct image *img);
 struct image *filter_contrast(struct image *img);
+int filter_count(struct image *img);
 
diff --git a/src/filters.c b/src/filters.c
index 126ad05..4cf1cd8 100644
--- a/src/filters.c
+++ b/src/filters.c
@@ -329,3 +329,25 @@ struct image *filter_contrast(struct image *img)
     return dst;
 }
 
+int filter_count(struct image *img)
+{
+    int histo[256];
+    int x, y, i, count = 0;
+    int r, g, b;
+
+    for(i = 0; i < 256; i++)
+        histo[i] = 0;
+
+    for(y = 0; y < img->height; y++)
+        for(x = 0; x < img->width; x++)
+        {
+            getgray(img, x, y, &r);
+            histo[r] = 1;
+        }
+
+    for(i = 0; i < 256; i++)
+        count += histo[i];
+
+    return count;
+}
+
diff --git a/src/main.c b/src/main.c
index 46f9129..beebc0c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -108,6 +108,7 @@ int main(int argc, char *argv[])
     {
         char *input = argv[optind], *result;
         struct image *img;
+        int count;
 
         img = image_load(argv[optind]);
         if(!img)
@@ -117,7 +118,9 @@ int main(int argc, char *argv[])
             continue;
         }
 
-        dprintf("image size %ix%i\n", img->width, img->height);
+        count = filter_count(img);
+        dprintf("image size %ix%i, %i colours\n",
+                img->width, img->height, count);
 
         if(!strcmp(mode, "test"))
             result = decode_test(img);
@@ -134,7 +137,8 @@ int main(int argc, char *argv[])
                 dprintf("autodetecting phpBB captcha\n");
                 result = decode_phpbb(img);
             }
-            else if(img->height == 25 || img->height == 30)
+            else if((img->height == 25 || img->height == 30)
+                     && count < 10)
             {
                 dprintf("autodetecting scode captcha\n");
                 result = decode_scode(img);