My customer wants content that is placed in DAM in authoring to be activated and moved to publish when it is placed in authoring. They are adding content using the Sling post servlet.
They been given the warnings: Each version is saved on publish and changing large files often will cause the repository to grow quickly.
Changing the default replication agent to be trigger by changed content does not seem to do the trick.
One of the way to automatically publish new content added to DAM would be modify dam workflow on author to include custom process step to activate the asset.
For version purging refer  and also make sure the workflow in publish is disabled.
Create a luncher in workflow console and select the following properties
Eventype : created
NodeType : dam:Assest
Path : /content/myweb/dam
Workflow : Publish Example
Activate : Enable
Exclude List : optional
Runmode : Author
luncher will automatically publish the newly added dam assests. I Hope it will help you