diff --git a/blocks/api/raw-handling/test/integration/google-docs-out.html b/blocks/api/raw-handling/test/integration/google-docs-out.html
index 8cb94dc1bbcb80..d8242c4779198e 100644
--- a/blocks/api/raw-handling/test/integration/google-docs-out.html
+++ b/blocks/api/raw-handling/test/integration/google-docs-out.html
@@ -60,6 +60,6 @@ <h2>This is a <em>heading</em></h2>
 <!-- /wp:paragraph -->
 
 <!-- wp:image -->
-<figure class="wp-block-image"><img src="https://lh4.googleusercontent.com/ID" /></figure>
+<figure class="wp-block-image"><img src="https://lh4.googleusercontent.com/ID" alt="" /></figure>
 <!-- /wp:image -->
 
diff --git a/blocks/api/raw-handling/test/integration/ms-word-online-out.html b/blocks/api/raw-handling/test/integration/ms-word-online-out.html
index 997359fa840372..d7d6370dfc3baf 100644
--- a/blocks/api/raw-handling/test/integration/ms-word-online-out.html
+++ b/blocks/api/raw-handling/test/integration/ms-word-online-out.html
@@ -50,5 +50,5 @@
 <!-- /wp:paragraph -->
 
 <!-- wp:image -->
-<figure class="wp-block-image"><img src="" /></figure>
+<figure class="wp-block-image"><img src="" alt="" /></figure>
 <!-- /wp:image -->
diff --git a/blocks/api/raw-handling/test/integration/ms-word-out.html b/blocks/api/raw-handling/test/integration/ms-word-out.html
index 3f4687910c6ce9..b5d2e6ba1ca548 100644
--- a/blocks/api/raw-handling/test/integration/ms-word-out.html
+++ b/blocks/api/raw-handling/test/integration/ms-word-out.html
@@ -85,5 +85,5 @@ <h2>This is a heading level 2</h2>
 <!-- /wp:paragraph -->
 
 <!-- wp:image -->
-<figure class="wp-block-image"><img src="" /></figure>
+<figure class="wp-block-image"><img src="" alt="" /></figure>
 <!-- /wp:image -->
diff --git a/blocks/library/gallery/index.js b/blocks/library/gallery/index.js
index 2fc8fbdf6344cf..5d208791144231 100644
--- a/blocks/library/gallery/index.js
+++ b/blocks/library/gallery/index.js
@@ -42,6 +42,7 @@ registerBlockType( 'core/gallery', {
 				alt: {
 					source: 'attribute',
 					attribute: 'alt',
+					default: '',
 				},
 				id: {
 					source: 'attribute',
diff --git a/blocks/library/image/index.js b/blocks/library/image/index.js
index 3a49ee6e8a416c..dbabc408dcd316 100644
--- a/blocks/library/image/index.js
+++ b/blocks/library/image/index.js
@@ -35,6 +35,7 @@ registerBlockType( 'core/image', {
 			source: 'attribute',
 			selector: 'img',
 			attribute: 'alt',
+			default: '',
 		},
 		caption: {
 			type: 'array',
diff --git a/blocks/test/fixtures/core__image.html b/blocks/test/fixtures/core__image.html
index 2a414855b03441..eda663561a38bf 100644
--- a/blocks/test/fixtures/core__image.html
+++ b/blocks/test/fixtures/core__image.html
@@ -1,3 +1,3 @@
 <!-- wp:core/image -->
-<figure class="wp-block-image"><img src="https://cldup.com/uuUqE_dXzy.jpg" /></figure>
+<figure class="wp-block-image"><img src="https://cldup.com/uuUqE_dXzy.jpg" alt="" /></figure>
 <!-- /wp:core/image -->
diff --git a/blocks/test/fixtures/core__image.json b/blocks/test/fixtures/core__image.json
index 89bdd5ba93cbc1..0aaa9b4804a968 100644
--- a/blocks/test/fixtures/core__image.json
+++ b/blocks/test/fixtures/core__image.json
@@ -5,8 +5,9 @@
         "isValid": true,
         "attributes": {
             "url": "https://cldup.com/uuUqE_dXzy.jpg",
-            "caption": []
+            "caption": [],
+            "alt": ""
         },
-        "originalContent": "<figure class=\"wp-block-image\"><img src=\"https://cldup.com/uuUqE_dXzy.jpg\" /></figure>"
+        "originalContent": "<figure class=\"wp-block-image\"><img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"\" /></figure>"
     }
 ]
diff --git a/blocks/test/fixtures/core__image.parsed.json b/blocks/test/fixtures/core__image.parsed.json
index 4e50ecd68576d5..eba958b3ec9a38 100644
--- a/blocks/test/fixtures/core__image.parsed.json
+++ b/blocks/test/fixtures/core__image.parsed.json
@@ -3,7 +3,7 @@
         "blockName": "core/image",
         "attrs": null,
         "innerBlocks": [],
-        "innerHTML": "\n<figure class=\"wp-block-image\"><img src=\"https://cldup.com/uuUqE_dXzy.jpg\" /></figure>\n"
+        "innerHTML": "\n<figure class=\"wp-block-image\"><img src=\"https://cldup.com/uuUqE_dXzy.jpg\" alt=\"\" /></figure>\n"
     },
     {
         "attrs": {},
diff --git a/blocks/test/fixtures/core__image.serialized.html b/blocks/test/fixtures/core__image.serialized.html
index fb41212fe367e1..bbe320d2bc1404 100644
--- a/blocks/test/fixtures/core__image.serialized.html
+++ b/blocks/test/fixtures/core__image.serialized.html
@@ -1,3 +1,3 @@
 <!-- wp:image -->
-<figure class="wp-block-image"><img src="https://cldup.com/uuUqE_dXzy.jpg" /></figure>
+<figure class="wp-block-image"><img src="https://cldup.com/uuUqE_dXzy.jpg" alt="" /></figure>
 <!-- /wp:image -->
diff --git a/blocks/test/fixtures/core__image__center-caption.html b/blocks/test/fixtures/core__image__center-caption.html
index 1973035e7c6e65..4fbce9c6fafd73 100644
--- a/blocks/test/fixtures/core__image__center-caption.html
+++ b/blocks/test/fixtures/core__image__center-caption.html
@@ -1,3 +1,3 @@
 <!-- wp:core/image {"align":"center"} -->
-<figure class="wp-block-image aligncenter"><img src="https://cldup.com/YLYhpou2oq.jpg"/><figcaption>Give it a try. Press the &quot;really wide&quot; button on the image toolbar.</figcaption></figure>
+<figure class="wp-block-image aligncenter"><img src="https://cldup.com/YLYhpou2oq.jpg" alt="" /><figcaption>Give it a try. Press the &quot;really wide&quot; button on the image toolbar.</figcaption></figure>
 <!-- /wp:core/image -->
diff --git a/blocks/test/fixtures/core__image__center-caption.json b/blocks/test/fixtures/core__image__center-caption.json
index c5465d7896235a..dfd4d57389ac5f 100644
--- a/blocks/test/fixtures/core__image__center-caption.json
+++ b/blocks/test/fixtures/core__image__center-caption.json
@@ -8,8 +8,9 @@
             "caption": [
                 "Give it a try. Press the \"really wide\" button on the image toolbar."
             ],
-            "align": "center"
+            "align": "center",
+            "alt": ""
         },
-        "originalContent": "<figure class=\"wp-block-image aligncenter\"><img src=\"https://cldup.com/YLYhpou2oq.jpg\"/><figcaption>Give it a try. Press the &quot;really wide&quot; button on the image toolbar.</figcaption></figure>"
+        "originalContent": "<figure class=\"wp-block-image aligncenter\"><img src=\"https://cldup.com/YLYhpou2oq.jpg\" alt=\"\" /><figcaption>Give it a try. Press the &quot;really wide&quot; button on the image toolbar.</figcaption></figure>"
     }
 ]
diff --git a/blocks/test/fixtures/core__image__center-caption.parsed.json b/blocks/test/fixtures/core__image__center-caption.parsed.json
index b32c1f8fd1a0fe..abd5611da19486 100644
--- a/blocks/test/fixtures/core__image__center-caption.parsed.json
+++ b/blocks/test/fixtures/core__image__center-caption.parsed.json
@@ -5,7 +5,7 @@
             "align": "center"
         },
         "innerBlocks": [],
-        "innerHTML": "\n<figure class=\"wp-block-image aligncenter\"><img src=\"https://cldup.com/YLYhpou2oq.jpg\"/><figcaption>Give it a try. Press the &quot;really wide&quot; button on the image toolbar.</figcaption></figure>\n"
+        "innerHTML": "\n<figure class=\"wp-block-image aligncenter\"><img src=\"https://cldup.com/YLYhpou2oq.jpg\" alt=\"\" /><figcaption>Give it a try. Press the &quot;really wide&quot; button on the image toolbar.</figcaption></figure>\n"
     },
     {
         "attrs": {},
diff --git a/blocks/test/fixtures/core__image__center-caption.serialized.html b/blocks/test/fixtures/core__image__center-caption.serialized.html
index 3dffbf76bc8418..7b7acfcd4d09d0 100644
--- a/blocks/test/fixtures/core__image__center-caption.serialized.html
+++ b/blocks/test/fixtures/core__image__center-caption.serialized.html
@@ -1,5 +1,5 @@
 <!-- wp:image {"align":"center"} -->
-<figure class="wp-block-image aligncenter"><img src="https://cldup.com/YLYhpou2oq.jpg" />
+<figure class="wp-block-image aligncenter"><img src="https://cldup.com/YLYhpou2oq.jpg" alt="" />
     <figcaption>Give it a try. Press the &quot;really wide&quot; button on the image toolbar.</figcaption>
 </figure>
 <!-- /wp:image -->