Image optimization

What it is. On-the-fly resizing, format conversion and compression. Billed per unique transformation — the combination of source image, width, quality and output format.

Why it is the most common cause of a bill that looks impossible.

Unique is doing a lot of work in that sentence. One source image requested at 40 widths, 3 qualities and 2 formats is 240 billable transformations.

An AI crawler or scraper walking query-string variants generates new combinations on every request. A widely-discussed Hacker News thread reported two crawlers sending 66,500 requests in a single day, with the author objecting that "$5 to resize 1,000 images is ridiculously expensive" — when the images were being resized for bots.

You can be billed thousands of transformations from a site with essentially no human visitors.

How to reduce it.

1. Bound the variants. Set images.qualities, images.formats and a restricted deviceSizes/imageSizes list in next.config.js. This turns an open-ended space into a small finite one, and it is the fix that actually works.
2. Rate-limit or firewall image routes. Most bot traffic is unsophisticated.
3. Pre-optimise static images at build time where you do not genuinely need on-the-fly transformation.
4. Block known crawlers you do not want in robots.txt and at the WAF — GPTBot, ClaudeBot, Bytespider and similar are the ones repeatedly named in these reports.