fix(astro:assets): add docs for missing imports and types

src/content/docs/en/guides/images.mdx

@@ -488,18 +488,7 @@ The [Astro template syntax](/en/reference/astro-syntax/) also supports writing a
 
 ### images in `src/`
 
-Local images must be imported from the relative path from the existing `.astro` file, or you can configure and use an [import alias](/en/guides/imports/#aliases). Then, you can access the image's `src` and other properties to use in the `<img>` tag.
-
-Imported image assets match the following signature:
-
-```ts
-interface ImageMetadata {
-  src: string;
-  width: number;
-  height: number;
-  format: string;
-}
-```
+Local images must be imported from the relative path from the existing `.astro` file, or you can configure and use an [import alias](/en/guides/imports/#aliases). They become available as an [`ImageMetadata` object](/en/reference/modules/astro-assets/#imagemetadata-1) giving you access to the image's `src` and other properties to use in the `<img>` tag.
 
 The following example uses the image's own `height` and `width` properties to avoid Cumulative Layout Shift (CLS) and improve Core Web Vitals: