I'm not sure if this is the best place to suggest this, but one thing it'd be great if Echo did: notify you when someone adds a photo you've created to a page on a wiki.

Echo currently notifies you when someone adds a link to a page you've created, so why not an image too? There's obviously a potential issue here with cross-wiki implementation. That is, I create an image and put it on Commons, and someone adds it to English Wikipedia - do I get the notification on Commons or English Wikipedia? As someone active on both, I'd be okay with either, really. But if someone adds it to, say, Farsi Wikinews, do I have to be active on there too in order to see the notification, or would having it so that gets passed to Commons be more useful?

That's an implementation detail. If I were notified every time images I'd created were used on one of the projects, I'm pretty sure that would motivate me to upload more images and make me feel happier about the work put into taking the photos and uploading them. I may also be able to help improve the article in which they are used or correct issues in said article, or thank the person using the image. Building up those relationships between image creators and article editors may lead to a bit less of a 'culture clash' and distrust between them.