I was going to make an in-depth, number-centric post on how I like to format pictures in OTs. It's still a bit specific, but the general theory can help create nice looking posts.
The short version is that if you design each line to be 1020 pixels you can divide that up into equal columns nicely to give everything a clean look. You could even get really crazy with the math as long as everything adds to 1020. This all works really well if you want to make rows for screenshots, gifs, pictures with text, or any combination of those. Granted, larger resolutions will allow typed text to extend past the pictures, so it might be better to start with a larger number, but then you'll need to combine each row into a single picture so that it scales correctly for everyone on desktop or mobile.
Long story short, math is your friend. If you work around a large number that is divisible by 2, 3, and 5, you can keep everything symmetrical:
The one quirk I've noticed is with spacing:
- You can't post pictures on multiple lines without there being a small space between them.
- You can't make a picture into a link without it adding small space on all sides. I played around with this last night, and found a way to still make nice rows, but it only works on desktop, so I'll spare the details there.
In both cases, you can no longer crop up a large picture and have it reassemble as a uniform picture.