Thanks for your question and for the outline of your application example. MLA can help you associate taxonomy terms such as “categories” in several different ways depending on the information contained I the image files and the method you use to upload them.
You wrote “the photos they upload are associated with the Dogs media category“. WordPress does not have a “media category” taxonomy. MLA adds taxonomy support to Media Library items and provides the “Att. Categories” taxonomy for your convenience. MLA can also add support for other taxonomies with the “Taxonomy Support” options on the Settings/Media Library Assistant General tab. Can you tell me which taxonomy you are using for your application?
One very common MLA application is to use the IPTC/EXIF metadata embedded in image files as a source for taxonomy terms. Do the image files in your application contain terms or keywords? If so, you can define a mapping rule to copy those values to taxonomy terms. Is that of interest?
You can assign terms to items as they are uploaded if you use the Media/Add New (Upload New Media) admin screen. MLA adds a “Bulk Edit Area” to that screen where you can specify terms to be assigned to items as they are uploaded. The “Bulk Edit Area” tab in the Help menu for that screen has more information. Would that work for your application?
MLA provides Quick and Bulk Edit areas on the Media/Assistant admin screen that you can use to assign terms to one or many items after they are uploaded. The “Bulk Actions” tab on the Help menu for that screen has more information. Would that be useful?
If you give me more details about your application and the upload process I can be more specific. I will leave this topic unresolved for now. Thanks for your interest in the plugin.