An image can affect loading work and layout stability in different ways. Explicit width and height tell the browser the image's aspect ratio before decoding finishes. Responsive CSS can then shrink the rendered box without losing that ratio. Deferring every image is also a mistake when the first image is the content the user came to see.
You'll render a small fictional media set. Keep the first image eager and mark secondary images for lazy loading. Give every image useful alternative text and intrinsic dimensions, then keep it within the preview width. The local data image makes the exercise independent of network availability. These checks establish concrete loading and layout properties; they do not claim a real-world speed increase without a measurement on the actual page and its visitors.