I'm creating ads on Propeller, for push, on Android devices. The ad creation interface recommends images of;
"Image (banner): 360 x 240 px; 720 x 480 px (for displays with high resolution, 720Kb maximum)"
However, doesn't look good on Android. See attached image, with cropped ad displayed to the right of the screen-shot.
So what's the best approach? Should we leave large areas on the top and bottom to be cropped off, and restrict our critical visual to the center of the image only? Do we need to shrink our creative, and put blank areas to the top and bottom? When you reduce the image, a lot of detail is lost, so the image could be less impactful.
How are most of you approaching image creation, what's the best way to have images that contribute to conversions? Any tips on how to have effective images, and an efficient ad creation work-flow?
I guess we have to allow for a lot of extra space at the top and bottom, then screw around with the Propeller-Ads rudimentary crop tool?
It seems awkward and unpredictable. Is there a better way?
Thanks for any advice with this - See attached photo.
The problem is that there are many different mobile devices out there so that the ad can look different form device to device.
My tip: Just skip the big images for now.
Especially when you´re still in test stage it´s good to keep the progress as simple as possible so that you can work more effective.
When you find a good campaign you can still test big images but even then I wouldn´t worry much if they look good in the preview or not.
Again, it can look different on different devices anyway so that it´s next to impossible to make a big image that looks same good on all devices.
Exception is probably when you just have a small image in the middle that can be seen on all devices.
Also don´t overestimate the average internet user, the people that see and click our ads.
When someone really believes that his device is randomly chosen to win a brandnew iPhone 12 so that he completes such offers you can be sure that these are not the smartest people out there 
Btw, would be great when you could insert the images properly in your posts.
In my signature is a link to a quick tutorial how to do it 
Once you crop a few images, you will understand how the cropping tool works and what part of the original image the important parts need to be in. Any cropping tools is limited in what it can do so simply feed it the format it works the best with 
It's never going to be perfect, especially with so many devices out there as twinaxe suggested above. So either try to do it as good as possible and format your images accordingly or skip using the large images.