How to Write Image Alt Text for SEO: A Practical Guide

Search engine bots are sophisticated, but they do not perceive visual information the same way humans do. They rely on metadata to interpret the subject matter of an image. Google Search Central recommends using descriptive, informative alt text that provides context for images and improves accessibility for visual content. When a bot crawls your page, it reads the alt attribute to understand how the image relates to the surrounding text. This relationship helps the algorithm determine the page’s authority on a specific topic. If you leave these attributes blank, you miss an opportunity to reinforce your primary keywords and provide a better user experience.

Accessibility is another major factor that search engines prioritize. Modern SEO is closely tied to user experience. Websites that are accessible to people using screen readers generally see better engagement metrics. Screen readers read the alt text aloud to the user. If the text is missing, the software might skip the image or read the filename, which is often unhelpful. By following these accessibility standards, you signal to search engines that your site is high-quality and inclusive. This can indirectly support your rankings because Google favors sites that provide a positive experience for all visitors, regardless of their physical abilities or technical limitations.

Writing effective alt text requires a balance between being specific and remaining concise. You should describe exactly what is shown in the image while naturally incorporating your target keywords. For example, if you have a photo of a blue ceramic mug on a wooden table, a poor alt tag would be alt=”mug”. A better version for SEO would be alt=”blue ceramic coffee mug sitting on a rustic wooden dining table”. This version is descriptive and provides context that helps a search engine understand the setting and the object. It also targets long-tail keywords that potential customers might use when searching for home decor or kitchenware.

Context is everything in the world of image optimization. If the same blue mug is part of a blog post about pottery techniques, your alt text should reflect that specific angle. You might write alt=”handcrafted blue ceramic mug showing the glazing texture after firing”. This helps the search engine understand that the image is relevant to a technical discussion about pottery, not just a lifestyle product shot. Avoid starting with phrases like “image of” or “picture of”. Both users and search engines already know it is an image. Use that space to provide more descriptive details instead.

• Be specific and describe the image content accurately.
• Keep the text under 125 characters to ensure it is fully read by screen readers.
• Integrate your primary or secondary keywords naturally without stuffing.
• Avoid using the same alt text for every image on a single page.
• Use a null alt attribute (alt=””) for purely decorative images like borders or spacers.

Keyword stuffing is one of the most frequent errors encountered in digital marketing audits. Website owners often try to pack every possible keyword into the alt attribute, which results in a poor experience for users and can be flagged as spam by search engines. For instance, an alt tag like alt=”shoes sneakers running footwear best shoes cheap sneakers for sale” is unhelpful. It does not describe the image and provides no value to a person using a screen reader. Instead, focus on a natural description like alt=”black leather running sneakers with white rubber soles”.

Another mistake is ignoring the filename of the image itself. While alt text is the primary focus, the filename provides secondary context. An image named IMG_5678.jpg with great alt text is less effective than an image named black-leather-running-sneakers.jpg. In a typical account audit, we often find that thousands of images have generic filenames. Fixing these alongside the alt text creates a consistent signal for search engine crawlers. Additionally, failing to update alt text after changing an image can lead to confusing metadata that contradicts the visual content on the page.

Yes, alt text is one of the most influential factors for appearing in Google Images. When users search for specific visual products or diagrams, Google relies heavily on the alt tag to decide which images to display. For e-commerce businesses, this can be a significant source of organic traffic. A Shopify store selling vintage watches can capture high-intent traffic by using alt tags like alt=”1960s vintage silver watch with leather strap”. This level of detail helps the image appear when a collector searches for that specific era or style. Without that tag, the image is essentially invisible to the search engine’s visual discovery engine.

Beyond direct rankings, optimized images can appear in the main search results page as part of an image pack. This happens when Google determines that a visual answer is the best response to a query. If you are writing a tutorial on how to tie a tie, and your step-by-step photos have excellent alt text like alt=”half-windsor knot step one crossing the wide end”, those images have a high chance of appearing at the top of the search results. This visibility can increase your click-through rate significantly compared to standard text links alone.

Not every image on a website needs a descriptive alt tag. Decorative elements, such as background patterns, icons that don’t add meaning, or horizontal lines, should have an empty alt attribute. This tells screen readers to ignore the image, which prevents the user from being bombarded with unnecessary information. If you use a magnifying glass icon next to a search bar, the alt text is redundant if the button is already labeled “Search”. In this case, alt=”” is the correct technical choice. This keeps the experience clean for visually impaired users.

Complex images like charts, graphs, or infographics require a different approach. A short alt tag is often insufficient to explain the data contained in a complex chart. For these assets, the alt text should provide a brief summary of the main takeaway, and a more detailed description should be provided in the surrounding text or via a link to a transcript. For example, if you have an infographic about market trends, your alt text might be alt=”Infographic showing a 20% increase in digital ad spend between 2023 and 2024″. This gives the user the most important data point even if they cannot see the full graphic.

• Use alt=”” for decorative icons or background images to improve screen reader flow.
• Summarize the main data point for complex infographics and charts.
• Ensure that functional images, like buttons with icons, have text that describes the action (e.g., alt=”Submit form”).
• Place detailed data descriptions in the body text near the image for better context.
• Avoid using text inside images; if you must, repeat that text in the alt attribute.