I published a module producing an image cropper UI built with Elm 0.18. I made it mostly as a learning exercise starting out with Elm more than a year ago. Goal was to build something to replace our (do not touch it might break) JS solution at work but never got around to it (soon!). I read in some thread a while ago that it is used in production by @hecrj which made me smile. Thanks for the trust! Would be happy to hear how it is working out for you!
I have now released an update compatible with Elm 0.19 also as a learning exercise (we have a few dependencies to go before we can upgrade our projects at work). This update was basically just make it build and function as previously. No improvement on API/code quality was considered. 
I will go forward and update it to use Browser.Dom, fix some issues I found and rethink the API/usage to try out Elm 19. Perhaps handle creation of the cropped image using canvas somehow…
Would be happy to receive any comments on anything!
https://package.elm-lang.org/packages/mikaxyz/elm-cropper/latest/
(To any package author: what is the recommended way to publish examples. I have included /examples with its own application elm.json in the package repo… Good/bad?)