Why blog images slow sites down, and how to fix it: formats, sizes and alt text

Blog posts without pictures look empty, but pictures carry a cost. A single uncompressed photo can weigh more than the whole text of an article. On a slow mobile connection that means an empty box where the image should be, a layout that jumps around and a visitor who leaves. Good images are part of performance and SEO, not only design.

Start with the right format

Use modern formats such as WebP or AVIF for photographs and illustrations, and keep SVG for logos and simple icons. Next.js can convert and serve modern formats automatically when you use the next/image component, which also resizes each image for the device that requests it.

Give every image a size

An image without a width and height makes the page jump as it loads. Give the browser the aspect ratio, for example with fill inside a container of fixed height, or by setting width and height. Add a sizes attribute so the browser downloads a file that fits the layout, not the largest version.

Load only what is visible

• Lazy-load images below the fold. Visitors who never scroll down should not have to download them.
• Mark the main image as a priority when it is the first thing visitors see, so it appears quickly.
• Compress originals before upload. Export at the size the image is displayed, or slightly larger for sharp screens, instead of uploading a 6000-pixel camera file.

Write alt text and file names for people

Alt text helps screen-reader users understand a picture and tells search engines what it shows. Describe the content in one short sentence, and leave it empty for purely decorative images. A file name such as blog-images-speed-seo.webp is far more useful than IMG_4831.jpg.

At Omnicode we keep cover images consistent and light, so every article loads fast and feels part of the same series. If you want a faster blog or website, let’s talk.