Short answer
An image CDN is a content delivery network that optimises, resizes and caches images close to users. An image CDN typically serves WebP or AVIF to browsers that accept those formats and falls back to JPEG elsewhere. For a DAM, the image CDN decides page speed and much of the egress cost once public channels pull renditions directly from the library.
How an image CDN works in a DAM
An image CDN sits between the DAM and every public channel, and answers image requests from edge servers near the user. The DAM storage acts as the origin, and the CDN only contacts it when an edge cache has no valid copy.
Four mechanisms decide how an image CDN behaves:
- Cache keys: the URL and selected headers that identify one cached version.
- Format negotiation: the browser's Accept header tells the CDN which formats it can display.
- Expiry and purge: time-to-live settings and purge calls decide when a cached copy is replaced.
- Access control: signed, expiring URLs restrict private or embargoed images.
Fact: HTTP caching rules, including freshness and the Vary header, are defined in RFC 9111. A custom domain on the CDN keeps image URLs under the buyer's own brand.
Example of an image CDN
Worked example: a webshop receives 50,000 product page views per day, and each page loads 6 images. That is 300,000 image requests per day.
At a 95% cache hit ratio, the origin serves 15,000 requests and the edge serves the rest. The DAM storage handles a fraction of the traffic, and pages load from a nearby server. The arithmetic is illustrative; real hit ratios depend on catalogue size and traffic patterns.
Image CDN in a DAM selection
An image CDN belongs at checkpoint 2, Define, where the buyer sets delivery and performance requirements. Cost belongs at checkpoint 6, Score, since egress and request fees grow with traffic.
Test these four behaviours at checkpoint 5, Test:
- Request one buyer image from two browsers and show the format each receives.
- Replace the master and measure the time until the CDN serves the new version.
- Expire the licence on an asset and show that its public URL stops serving.
- Show the custom domain setup and the egress line on a sample invoice.
DAMSelection assessment: test licence expiry on cached URLs, because a cached image keeps serving after the DAM record expires unless the platform purges it. Model traffic in the TCO calculator and read the total cost of ownership guide.
Common mistakes with an image CDN
Image CDN setups go wrong through four common mistakes.
- Missing purge rules for rights expiry and embargo, so restricted images stay public.
- Publishing on a vendor subdomain, which ties image URLs and search rankings to one supplier. The exit strategy guide covers URL ownership.
- Leaving egress out of the cost model.
- Stacking two CDNs without a clear cache owner, which doubles purge work.
Related terms: Dynamic media, Rendition.
Frequently asked
Does a DAM need a separate image CDN?
A DAM needs a separate image CDN only when its own delivery layer misses requirements on formats, regions, custom domains or cost. Many platforms include a CDN, and others integrate with one. Compare both options on the same traffic model before deciding.
What happens to cached images when a licence expires?
A cached image keeps serving until its time-to-live ends or the DAM sends a purge request. Ask each vendor to show automatic purging on licence expiry in the demo, with the delay in minutes.