Check images

examples/markdown.feature

@@ -92,4 +92,4 @@ Feature: Markdown
     linkcheck -v foo.md 2>&1 | wc -l
     """
     When I successfully run `sh foo.sh`
-    Then the stdout should contain exactly "2"
+    Then the stdout should contain exactly "4"

main.go

@@ -49,13 +49,23 @@ func extractURLs(n *html.Node) []string {
 		n := ns[i]
 		ns = ns[:i]
 
-		if n.Type == html.ElementNode && n.Data == "a" {
+		if n.Type == html.ElementNode {
+			switch n.Data {
+			case "a":
 				for _, a := range n.Attr {
 					if a.Key == "href" && isURL(a.Val) {
 						ss[a.Val] = true
 						break
 					}
 				}
+			case "img":
+				for _, a := range n.Attr {
+					if a.Key == "src" && isURL(a.Val) {
+						ss[a.Val] = true
+						break
+					}
+				}
+			}
 		}
 
 		for n := n.FirstChild; n != nil; n = n.NextSibling {