Image alt text for SEO is a descriptive text attribute added to an HTML image tag that informs search engines and screen readers about the visual content. Google uses alt text alongside computer vision algorithms and the surrounding page context to categorize images correctly. By implementing clear and concise descriptions, you help search engines index your media assets accurately while ensuring your digital content remains accessible to all users.
Why is image alt text essential for your website?
The primary function of alt text is accessibility. Users who rely on screen readers depend on these text descriptions to understand what an image depicts. When an image fails to load, the alt text also appears as a placeholder, providing context to the visitor.
From a search engine perspective, alt text acts as a bridge. While computer vision has improved, it cannot always interpret the specific intent or subject matter of a complex photograph or diagram. Providing manual, descriptive alt text ensures that your images contribute to the overall relevance of your page for specific search queries.
What makes an alt text description effective?
An effective alt text is descriptive, specific, and relevant to the content on the page. Avoid keyword stuffing, as this creates a negative experience for both users and search engines. Instead, focus on describing the image as if you were explaining it to someone who cannot see it.
Characteristics of high-quality alt tags
- Be specific: Describe the subject, action, or context shown in the image.
- Be concise: Keep the text under 125 characters to ensure compatibility with most screen readers.
- Be relevant: Use terms that relate to the surrounding page copy.
- Avoid filler: Do not include phrases like ‘image of’ or ‘picture of’ as this is redundant for screen reader users.
How do you write alt text for different types of images?
Different images require different approaches. A product photo on a Shopify store needs a different description than a decorative background element. For instance, if you are selling a blue leather handbag, the alt text should specify the product type, color, and material. If the image is a generic design element, it may not require descriptive text at all.
Handling decorative vs. functional images
- Product images: Include the brand, product name, and key visual attributes.
- Informational images: Summarize the data or the main point of the image.
- Decorative images: Use an empty alt attribute (alt=””) to tell screen readers to skip the element.
- Text in images: Transcribe the text exactly if it serves a functional purpose.
Can you use keywords in your image alt text?
You can include relevant keywords, but they must appear naturally within the description. If your page is about mountain biking, an alt text like ‘mountain biker riding down a rocky trail’ is excellent. It describes the scene accurately while naturally incorporating the keyword.
Avoid creating lists of keywords in your alt tags. If you have an image of a running shoe, do not label it as ‘running shoe, best running shoe, cheap shoe, athletic footwear.’ This practice triggers spam filters and provides no value to users. Stick to one clear, human-readable sentence.
Where do you implement alt text in your CMS?
Most content management systems make it easy to add alt text. In WordPress, you can find the ‘Alt Text’ field in the Media Library or within the Block Editor when you select an image. In Shopify, you typically edit this within the product or collection page media settings.
If you are editing the raw HTML, the syntax is straightforward. You add the alt attribute directly inside the image tag, such as: 
. Always ensure you close your quotes correctly.
How to audit your site for missing alt text
Running a site audit is the best way to find missing or poor alt tags. You can use tools like Screaming Frog or the built-in audit features in Google Lighthouse. These tools will flag images that lack alt attributes, allowing you to prioritize the most important pages on your site.
In a typical account, fixing alt text for your top 20% of traffic-driving pages provides the most significant impact. Start with your product pages, service landing pages, and blog posts that feature original photography or diagrams. Do not worry about fixing thousands of legacy images at once; prioritize those that appear in search results.
Where to start this week
Start by identifying the ten images on your website that appear on your highest-trafficked pages. Open these pages and inspect the images using your browser’s developer tools or your CMS media editor. Check if the alt text exists, and if it does, assess whether it is descriptive and free of keyword stuffing.
Once you have updated these ten images, move on to the next set. By dedicating just thirty minutes a week to this task, you will create a habit that improves both your accessibility standards and your search performance. Remember that Alien Road focuses on the long-term benefit of these small, consistent content updates.
Consistency remains the most important factor in SEO. When you upload new images, make it a standard part of your workflow to write the alt text before hitting publish. This prevents a backlog of unoptimized images and ensures that every new piece of content you add meets your accessibility goals from day one.
Keep in mind that alt text is just one part of your image optimization strategy. Ensure your image file names are descriptive, such as ‘red-leather-tote-bag.jpg’ rather than ‘IMG_001.jpg’. When you combine descriptive file names with precise alt text, you provide search engines with the best possible data to understand your content.
Finally, monitor your site’s performance through Google Search Console to see if your image search traffic shifts over time. While results do not happen overnight, providing clear context is a foundational step in building a site that is both user-friendly and search-engine-ready. Keep refining your approach based on the specific needs of your audience.
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