Images are create-able via plugins using the SDK - and each user would have to load them.
If you plan on using the REST API - plan that what you widgets you want to CRUD - be the: sticker (sticky note), shape, text, line or card — as you can see in the image above.
The benefit of the REST API is that the above reads and writes can happen from the REST API app centrally/globally from/to many boards. But the write capabilities are much lower than the SDK. The SDK, on the other hand, has to be activated local to each user/board. The SDK plugins can be installed across a team of users - so that they show up for any member of that team - each member authorizes the permission scopes they allow for the plugin- but they do that only once per plugin
In a general sense the REST API is designed for working on and with boards - and the SDK is designed for working in boards on widgets.