Collections imported from AEM on-demand portal to AEM instance does not import images attached to collection. The same is behavior with articles. These collections and articles are non-editable in AEM as a result one cannot work on those collections and articles.
You may get more details from the product team on this but I believe AEM only shows you the collection or article images that have been created from within the AEM instance. The collection import allows you to add new content you generate in AEM to an existing structure you already had in place.
Same for Edits, AEM runs template-based authoring so would only be able to modify content based on these templates.
When you're using AEM to author content for AEM Mobile, I think the best approach is edit images only where you create them. If you create the article or collection in the Portal, edit it in the Portal, not in the AEM authoring instance. Similarly, if you create a collection or article in AEM, don't edit the image in the Portal.