Fixed duplicate images in Outlook for dark/light mode

refs https://github.com/TryGhost/Team/issues/2671

The inline style display: none; isn't applied to the images in Outlook for some reason. This change manually removes the images in the backend.

ghost/email-service/lib/email-renderer.js

@@ -346,6 +346,17 @@ class EmailRenderer {
             }
         });
 
+        // Remove duplicate black/white images (CSS based solution not working in Outlook)
+        if (templateData.backgroundIsDark) {
+            $('img.is-light-background').each((i, elem) => {
+                $(elem).remove();
+            });
+        } else {
+            $('img.is-dark-background').each((i, elem) => {
+                $(elem).remove();
+            });
+        }
+
         // Convert DOM back to HTML
         html = $.html(); // () Fix for vscode syntax highlighter
 

ghost/email-service/test/email-renderer.test.js

@@ -855,7 +855,7 @@ describe('Email renderer', function () {
     });
 
     describe('renderBody', function () {
-        let renderedPost = '<p>Lexical Test</p>';
+        let renderedPost = '<p>Lexical Test</p><img class="is-light-background" src="test-dark" /><img class="is-dark-background" src="test-light" />';
         let postUrl = 'http://example.com';
         let customSettings = {};
         let emailRenderer;
@@ -1195,6 +1195,52 @@ describe('Email renderer', function () {
             response.plaintext.should.containEql('Test footer');
         });
 
+        it('works in dark mode', async function () {
+            const post = createModel(basePost);
+            const newsletter = createModel({
+                header_image: null,
+                name: 'Test Newsletter',
+                show_badge: false,
+                feedback_enabled: true,
+                show_post_title_section: true,
+                background_color: '#000000'
+            });
+            const segment = null;
+            const options = {};
+
+            let response = await emailRenderer.renderBody(
+                post,
+                newsletter,
+                segment,
+                options
+            );
+
+            assert.doesNotMatch(response.html, /is-light-background/);
+        });
+
+        it('works in light mode', async function () {
+            const post = createModel(basePost);
+            const newsletter = createModel({
+                header_image: null,
+                name: 'Test Newsletter',
+                show_badge: false,
+                feedback_enabled: true,
+                show_post_title_section: true,
+                background_color: '#FFFFFF'
+            });
+            const segment = null;
+            const options = {};
+
+            let response = await emailRenderer.renderBody(
+                post,
+                newsletter,
+                segment,
+                options
+            );
+
+            assert.doesNotMatch(response.html, /is-dark-background/);
+        });
+
         it('replaces all links except the unsubscribe and feedback links', async function () {
             const post = createModel(basePost);
             const newsletter = createModel({