I am trying to strip off the metadata from the original rendition of a uploaded image in DAM or compress it to reduce the size.
Are there any AEM out of the box APIs to accomplish this? I am trying to put the behaviour in a workflow process step in AEM 6.2.
The recommended way for modifying DAM metadata is to use custom workflows.
If you are trying to modify the meta-data persisted within the file (for example some image files have location and copyright information) then you will need to use one of many API's available in the libraries shipped with AEM or use 3rd party libraries.
Alternatively, if you want to change the meta data persisted with you DAM asset, you will need to use your custom workflow to update/modify the meta data that is extracted from the DAM assets.
Either way, a lot of this depends on what metadata you are planning to extract or modify and this will have an impact on whether you can use builtin libs or 3rd party libs.