As far as I know lepozepo:s3 uploading files directly to amazon s3 which is good for large files but I wouldn't recommend to use it for images (avatars) uploads because you need to transform it and make sure that it's actually image and not broken (and nobody trying to hack you :D )
If you still want to use lepozepo:s3 then you should google canvas image manipulation on client side. There are some meteor packages that doing resize and crop on client so you will get the idea. Maybe with canvas you would be able to auto-orient images https://github.com/thinksoftware/meteor-image-resize-client
Also there are some AWS Lambda project that can help you with transforming images on s3 bucket but I don't know how to set it up.
Second option is to upload images through your meteor server that will transform it the way you want. I'm using CollectionFS package. It's not perfect but right now there is no ideal solution for file uploads in meteor.
I guess.. Ideally you need to run separate server for image uploads but who wants to deal with it :D