Image SEO Checker

Images account for a significant portion of total page weight on most websites -- often 50% or more of all downloaded bytes. Yet image optimization remains one of the most overlooked aspects of search engine optimization. When done correctly, image SEO improves your page load speed, enhances accessibility, drives additional traffic through Google Image Search, and strengthens your overall ranking signals. When neglected, unoptimized images slow down your site, create poor user experiences, and leave substantial organic traffic on the table.

Google processes billions of image search queries every day, and Google Image Search is the second largest search engine in the world by query volume. Optimizing your images is not just about making your pages faster -- it opens up an entirely separate traffic channel that most SEO strategies ignore. The images on your product pages, blog posts, and service pages can each become an entry point for new visitors.

Alt Text: The Foundation of Image SEO

Alt text (alternative text) is the single most important image SEO element. It serves a dual purpose: providing a text description for users who cannot see the image (screen reader users, users with images disabled, or when images fail to load) and telling search engines what the image depicts. Google has explicitly stated that alt text is a primary signal used to understand image content for both web search and image search rankings.

Writing effective alt text requires balancing descriptiveness with brevity. The ideal alt text is under 125 characters, accurately describes the image content, and includes relevant keywords naturally without stuffing. For example, instead of writing alt="shoes" for a product image, write alt="Nike Air Max 270 running shoes in black and white". Instead of alt="team meeting office collaboration workspace productivity", write alt="Marketing team reviewing quarterly campaign results in conference room".

Decorative images that serve no informational purpose -- such as background patterns, spacer images, or purely aesthetic flourishes -- should use an empty alt attribute (alt=""). This signals to screen readers that the image can be skipped, improving the experience for assistive technology users. This checker flags empty alt attributes so you can verify each one is intentionally decorative rather than accidentally empty.

Image Dimensions and Cumulative Layout Shift

Cumulative Layout Shift (CLS) measures how much your page layout moves unexpectedly during loading. Images without explicit width and height attributes are a leading cause of poor CLS scores because the browser does not know how much space to allocate until the image downloads. When the image arrives, surrounding content shifts to make room, creating a jarring user experience and hurting your Core Web Vitals scores.

The fix is straightforward: always include width and height attributes on your img tags. Modern browsers use these attributes to calculate the aspect ratio and reserve the correct space before the image loads. Combined with CSS like max-width: 100% and height: auto, your images will be both responsive and layout-stable. This single change can dramatically improve your CLS score.

Modern Image Formats and Compression

The image format you choose has a direct impact on file size and loading speed. Legacy formats like JPEG and PNG have been the web standard for decades, but WebP and AVIF offer dramatically better compression at equivalent visual quality. WebP files are typically 25-35% smaller than JPEG, and AVIF can achieve 40-50% size reductions. Since image bytes are often the largest contributor to page weight, switching formats is one of the fastest ways to improve load times.

The HTML picture element makes it easy to serve modern formats with automatic fallbacks. You can offer AVIF as the primary source, WebP as the secondary, and JPEG as the fallback -- the browser automatically selects the best format it supports. For sites using a CDN or image optimization service, format conversion can often be handled automatically without changing your source images.

Lazy Loading and Performance

Native lazy loading with the loading="lazy" attribute tells the browser to defer downloading off-screen images until the user scrolls near them. This reduces initial page load time, decreases bandwidth consumption, and improves Largest Contentful Paint (LCP) by allowing the browser to prioritize above-the-fold content. Every major browser supports native lazy loading, making it a zero-JavaScript performance optimization.

One important nuance: do not lazy load your hero image or other above-the-fold images. These should load immediately to achieve the fastest possible LCP. Only apply lazy loading to images below the fold -- product thumbnails in a grid, images further down in an article, sidebar images, and footer logos. Some developers add loading="lazy" to every image indiscriminately, which actually hurts LCP by delaying the most important visual content.

Descriptive Filenames for Better Indexing

Before Google even reads your alt text, it looks at the image filename as a signal for content understanding. A file named "blue-ceramic-coffee-mug.webp" provides clear context, while "DSC_0047.jpg" or "a7f3b2c1d4e5.png" tells Google nothing useful. Descriptive filenames use hyphens to separate keywords and accurately describe the image subject.

Image optimization is a foundational part of technical SEO. If you need help implementing image optimization at scale across your entire site -- including format conversion, responsive images, CDN configuration, and alt text auditing -- our team can handle the complete implementation as part of a comprehensive SEO audit and remediation plan.