Well one particular use case I know of where it could be useful is that many people who work in marketing need images for campaigns. It doesn't have to be too high resolution or anything just simple 600px wide images for facebook or twitter.
Now since marketing is run by marketers and they don't necessary know Photoshop or image editing software, they could use some simple tool which lets them drag drop images, text etc with intelligent spacing and margins.
Once they have put images, text in order they want they can get a screenshot of the canvas which they can use for campaigns. My girlfriend is a community manager with a digital agency and she would kill to have a simple tool like this. Since you already have something similar you just need to add option to export the screenshot of canvas to be used for campaigns.
I wish I could help but I am more of UI/UX designer than developer and currently working my ass off on some client projects.
Or do you mean image manipulation itself? If you are good at it, you should join us! We'd love to have you open source it. :)