Unlike other websites, here you can adjust what photo previews focus on.
All you have to do is click 'edit' after you select your photo for uploading. This is where you can add your #AltText as well. Drag the circle over the area you want to be the focus. Apply your changes, and voila. No more awkward crops on inappropriate areas!
Note, these screenshots were from the fancy web version, so things may be slightly different on the apps, but hopefully they help.