🐛 Koenig - Fixed missing `alt` text on images

refs https://github.com/TryGhost/Ghost/issues/9724
- render `alt` attribute if the image card payload has an `alt` property

core/server/lib/mobiledoc/cards/image.js

@@ -20,6 +20,9 @@ module.exports = {
         let img = dom.createElement('img');
         img.setAttribute('src', payload.src);
         img.setAttribute('class', 'kg-image');
+        if (payload.alt) {
+            img.setAttribute('alt', payload.alt);
+        }
 
         figure.appendChild(img);
 

core/test/unit/lib/mobiledoc/cards/image_spec.js

@@ -31,6 +31,20 @@ describe('Image card', function () {
         serializer.serialize(card.render(opts)).should.eql('<figure class="kg-image-card"><img src="https://www.ghost.org/image.png" class="kg-image"><figcaption>Test caption</figcaption></figure>');
     });
 
+    it('renders an image with alt text', function () {
+        let opts = {
+            env: {
+                dom: new SimpleDom.Document()
+            },
+            payload: {
+                src: 'https://www.ghost.org/image.png',
+                alt: 'example image'
+            }
+        };
+
+        serializer.serialize(card.render(opts)).should.eql('<figure class="kg-image-card"><img src="https://www.ghost.org/image.png" class="kg-image" alt="example image"></figure>');
+    });
+
     it('renders nothing with no src', function () {
         let opts = {
             env: {