Image SEO for bloggers: alt text, size and format

Search engines cannot see a picture the way a reader can, so they judge your images by three things: the words around them, their file size, and their format. Get those three right and your images help your posts twice over — they make the page load faster, and they give search engines more reason to show your post for image and web searches. The work takes a few minutes per image, and every step below can be done in your browser on ImageTool.us, with no upload and no signup.

1. Alt text: describe the image, not the keyword

Alt text is the short description that sits in the image's alt attribute. Screen readers read it aloud, browsers show it if the image fails to load, and search engines use it to understand what the image shows. Good alt text describes the picture in plain words, in one sentence, as if you were telling someone who cannot see it.

• Describe what is actually in the image: "a sliced sourdough loaf on a wooden board" beats "bread recipe image".
• Use your post's topic naturally when it fits the picture — forced repetition reads as spam to readers and search engines alike.
• Give every image its own alt text. Copying the same sentence onto ten images tells a search engine nothing new about any of them.
• Leave decorative images empty (alt="") so screen readers skip them instead of announcing a meaningless description.
• Keep it short — roughly 125 characters or fewer is a sensible ceiling, because longer text gets cut off by some screen readers.

2. File names: rename before you upload

A file named IMG_4821.jpg says nothing to anyone. Rename it to something descriptive, with words separated by hyphens, before uploading: sourdough-loaf-wooden-board.jpg. Search engines read file names, and a descriptive name also makes your media library far easier to search later. Rename the file on your own device first; renaming after upload is possible on most blogging platforms, but it is an extra step that is easy to forget.

3. Size: resize, then compress, then upload

Page speed is part of how search engines rank a post, and oversized images are the most common reason a blog post loads slowly. A photo straight from a phone can be 4000 pixels wide and several megabytes, while the column it sits in is rarely wider than 800 to 1200 pixels. Uploading the full-size file wastes most of those pixels and makes every reader wait.

Do the work in this order. First, use the Image Resizer to bring the photo down to the width your blog actually displays — around 1200 pixels is a good default for a full-width blog image, or 1920 x 1080 if the post needs a larger hero image. Second, compress the resized copy with the Image Compressor, or aim at an exact size with Compress Image to 200KB or Compress Image to 100KB for smaller in-post images. For how far quality can drop before the loss shows, see the guide to compressing images without losing quality. Resize first and compress second: compressing a full-size photo and resizing it afterwards means doing the work twice.

4. Format: match the format to the picture

The right format can halve a file's size with no visible change. The short version: JPG for photographs, PNG for graphics and anything needing transparency, WebP as the modern all-rounder where your platform supports it. The Image Converter switches between formats in one step, and the JPG to WebP Converter and PNG to WebP Converter cover the most useful upgrades. If a PNG photo is far larger than it needs to be, the PNG to JPG Converter usually fixes it in seconds, provided the image has no transparency to preserve — see the transparent PNG guide before converting a logo or graphic. For the full decision table, read the guide to the best image format and the JPG vs PNG vs WebP guide.

5. Context: captions and surrounding text matter too

Search engines also read the words near an image. A caption under a photo is a natural place to add a sentence of genuinely useful detail — where the photo was taken, what it shows, or why it matters to the post. The paragraph immediately around the image should mention the same topic in normal language. This is not a trick to game: it is simply how a well-written post already behaves, and it is why an image dropped into an unrelated paragraph ranks for nothing.

6. One more setting: lazy loading

Lazy loading tells the browser to load images only when the reader scrolls near them, so the first screen of a long post appears faster. Most blogging platforms now switch this on by default, so check your platform's settings rather than installing anything new. It changes nothing about the image files themselves — it only changes when they load — but on image-heavy posts the speed difference is noticeable, especially on mobile connections.

Common mistakes

• Uploading full-size phone photos and letting the blog theme shrink them visually — the reader still downloads the full file.
• Leaving alt text blank on every image, or writing the same keyword-stuffed sentence on all of them.
• Keeping camera file names like IMG_4821.jpg instead of descriptive names.
• Using PNG for every photograph, when JPG would be a fraction of the size.
• Compressing a photo so far that text in screenshots becomes unreadable.
• Re-saving a JPG many times — each save loses a little quality, so optimise once, from the original.
• Adding images that have nothing to do with the post, just to fill space.

Quick checklist

• Renamed the file descriptively, with hyphens between words.
• Written unique, plain-language alt text for every meaningful image.
• Resized the image to the width the blog actually displays.
• Compressed it to a sensible size, and kept the original file untouched.
• Picked the right format: JPG for photos, PNG for graphics and transparency, WebP where supported.
• Added a caption or a relevant sentence near images that need context.
• Confirmed lazy loading is on for long, image-heavy posts.

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