This is not currently possible with the ICEmobile API, and the ability for the web application to save a file to an arbitrary location on the device is potentially a security issue. So, it would be necessary to define a restricted, secure version of this feature for it to be added to ICEmobile open source (such as either allowing the user to browse to the location, or specifying the save location to be a well-known location for photos).
Since this is a feature request and does not have an "answer", please contact product.support@icesoft.com or post on the ICEmobile forums to discuss further. Once that discussion is complete, the final result can be posted here as an answer.