There's a funny back story on today's #fmsphotoaday / #project365 photo. I am holding the phone with my left hand, and I am a lefty, and I am shooting with my right hand, and I have had a lot of coffee today.
One way to mitigate would be to put the camera on a tripod, use the remote and concentrate on getting the tripod aimed properly, then it is a matter of keeping a consistent position for my hand until I got the shot right. Add to that I was feeling too lazy to add a circular polarizer filter, so the hand had to angle the phone just right to avoid reflections from the lights above.
That of course is too much work. It was easier to just get the focus effect right and adjust for geometry later, which is more or less what I did.
The left shot is as-is, notice that the phone looks distorted because I couldn't get it perfectly parallel to the focal plane of the camera. The middle shot is the result of adding keystone distortion adjustments to the left image, I did this with DxO ViewPoint. The way this works is you pick four corners of an object that represents a diamond shape with 90 degree corners. The photo is rotated because the program assumes that you are aligning yourself to a horizon.
The right crop is the maximum rectangle that you can crop from the second photo (plus some extra processing that doesn't involve geometry) automatically. You can constraint the crop rectangle to the original aspect ratio, but it would had cut some of the phone, the way you fix this (something I screwed up) is that if you know you will be doing keystone adjustments, you should try to give yourself as much room around the object as it is possible. Had I shot this a bit farther and had as much as one inch of extra room, I could have kept the original aspect ratio.