Add image reset styles.

blank-canvas-blocks/assets/ponyfill.css

@@ -15,6 +15,11 @@ p {
 	margin: 0;
 }
 
+img {
+	height: auto;
+	max-width: 100%;
+}
+
 /**
  * Required Variables
  */

blank-canvas-blocks/sass/base/_normalize.scss

@@ -12,4 +12,10 @@ body {
 
 p {
   margin: 0;
+}
+
+// Needed until https://github.com/WordPress/gutenberg/pull/27518/ is merged.
+img {
+	height: auto;
+	max-width: 100%;
 }