A hero image is a large, prominent visual at the top of a webpage designed to grab attention, set the mood, and convey a brand’s core message. Its defining features include being visually engaging, high-quality, and often full-width, while best practices involve ensuring the text is readable, the image is responsive, it includes a clear call-to-action (CTA), and is optimized for fast loading speeds.
Defining features

Large and prominent:
Typically spans the width of the screen and sits above the fold, making it the first thing a visitor sees. 

High-quality visual:
Can be a high-resolution photo, engaging video, animated illustration, or image slider.
Key message conveyor:
Intended to quickly communicate the brand’s value proposition or a key message with minimal text.
Creates a first impression:
Acts as a digital “book cover,” setting the tone and emotional atmosphere for the user experience.
Guides the user:
Can be used to visually guide visitors to other important parts of the page, such as a CTA button.

Best practices

Prioritize readability:
Ensure any overlaid text is easy to read using contrast, shadows, or semi-transparent overlays, and avoid a busy background. 

Include a strong CTA:
Use a concise and compelling call-to-action to prompt visitors to take the next step (e.g., “Shop Now,” “Get Started”).
Ensure it’s responsive:
Design the image to look good on all screen sizes, from large desktops to small mobile phones, as over half of web traffic is mobile.
Optimize for speed:
Use high-quality, but compressed, images to ensure the page loads quickly. Slow loading times can cause users to leave.
Focus on a single message:
Avoid clutter by focusing on conveying one core idea, concept, or offer.
Maintain brand consistency:
Use colors and visuals that align with the rest of the website’s branding for a cohesive look.
Use proper sizing:
Aim for a desktop width of around 1200-1600 pixels with a 16:9 aspect ratio, but adjust based on your specific needs.