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Technical SEO

SEO PNG

PNG (Portable Network Graphics) is a lossless image format that preserves quality and supports transparency, used for web graphics and screenshots.

Also called
Portable Network Graphics
Applies to
Web images, graphics, logos, screenshots
Commonly confused with
JPEG, WebP, AVIF

Key points

  • PNG is lossless, so it retains sharp edges and transparency for logos, icons, and screenshots.
  • Using PNG for large photos can bloat page size and slow load times, hurting Core Web Vitals.
  • Google recommends descriptive filenames, alt text, and image sitemaps for all image formats.
  • Modern formats like WebP and AVIF often deliver smaller files than PNG with comparable quality.
  • Uncompressed PNG files waste bandwidth and reduce crawl efficiency.

How it works

PNG uses lossless compression, meaning every pixel is preserved exactly when the file is saved and opened. This makes it ideal for images with sharp text, solid colours, or transparent backgrounds, where any quality loss would be noticeable. The format supports alpha channels, so parts of an image can be fully or partially transparent.

Google Search supports PNG images in HTML img elements and indexes them when proper SEO practices are followed. To help crawlers understand the image, Google recommends using descriptive, hyphen-separated filenames and relevant alt text. Responsive images and image sitemaps further aid discovery and indexing.

Because PNG files are often larger than lossy alternatives, page speed can suffer if they are used carelessly. Page speed is a ranking factor and affects user experience, so choosing the right format matters for both performance and crawl efficiency.

Common mistakes

  • Using PNG for large photos when JPEG, WebP, or AVIF would usually be smaller and faster, slowing page load and hurting Core Web Vitals.
  • Uploading uncompressed PNG files, which can bloat page size and reduce crawl efficiency.
  • Leaving filenames generic (e.g., image1.png) instead of descriptive and hyphen-separated, missing an opportunity for image seo.
  • Relying on PNG alone without adding alt text, responsive images, or image sitemaps, limiting discoverability and indexing.
Read next Image SEO The image seo page explains how to optimise all image formats for search, including filenames, alt text, and sitemaps, building on the format basics covered here.
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Sources

  1. Google Search Central – Image SEO best practices Primary source for how Google handles image discovery, indexing, supported formats, alt text, filenames, and image sitemaps.
  2. Google Search Central – Image publishing guidelines Authoritative guidance on image file formats, landing pages, and preferred images for structured data and og:image.
  3. Screaming Frog – Image SEO Clear practitioner-oriented overview of image optimization for relevance, indexability, and performance.
  4. SEO Analyse – PNG definition Concise definition of PNG as a lossless, transparency-supporting format.

Written and maintained by Nora Lindholm. Last updated 27 July 2026.

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