Fix issue #183 image.itemtype

lib/template.html

@@ -223,7 +223,16 @@
 {% endif %}
 
 {% if seo_page_image %}
+  {% if page.image.height && page.image.width %}
+    "image": {
+        "@type": "ImageObject",
+        "url": {{ seo_page_image | jsonify }},
+        "height": {{ page.image.height | jsonify }},
+        "width": {{ page.image.width | jsonify }}
+    },
+  {% else %}
     "image": {{ seo_page_image | jsonify }},
+  {% endif %}
 {% endif %}
 
 {% if page.date %}

spec/jekyll_seo_tag_spec.rb

@@ -195,6 +195,10 @@ describe Jekyll::SeoTag do
           expected = %r!<meta property="og:image" content="http://example.invalid/img/foo.png" />!
           expect(output).to match(expected)
         end
+
+        it "outputs the default image JSON item" do
+          expect(json_data["image"]).to eql("http://example.invalid/img/foo.png")
+        end
       end
 
       context "when given a facebook image" do
@@ -225,6 +229,12 @@ describe Jekyll::SeoTag do
           expected = %r!<meta property="og:image:width" content="2" />!
           expect(output).to match(expected)
         end
+
+        it "outputs the default image JSON object with dimensions" do
+          expect(json_data["image"]["url"]).to         eql("http://example.invalid/img/foo.png")
+          expect(json_data["image"]["height"]).to eql(1)
+          expect(json_data["image"]["width"]).to eql(2)
+        end
       end
     end