As @max-gasner mentioned, it’s common for latest to be tracking the master branch of a git repository. This allows the engineers to quickly build and test images before they are released and version tagged. This is one of the reasons why it’s not recommended to ever use latest tags for anything critical where you need reproducibility.
jaegertracing/jaeger-agent:latest doesn’t have any other tags so the only way to determine which “version” of latest you are using is to look at the digest. This uniquely identifies the image build. Tags actually resolve to digests. So when a new image is built with the latest tag, that tag will then resolve to the digest of the new image.
DockerHub only shows the short version. You can inspect the full digest like this:
docker image inspect --format '{{.RepoDigests}}' jaegertracing/jaeger-agent:latest
> [jaegertracing/jaeger-agent@sha256:bacc749faba325fbe39dc13294c2222fb0babc9ecd344c25d9d577720a80b5ca]