If you don't wish to use Minecraft's screenshot system, use Gyazo. Look up "Gyazo for <your OS name here, so Windows/Mac/Linux>". Download that, and then there ya have it. Also, for screenshots on Minecraft, some laptops with the (Fn) key require you to use the shortcut (Fn)+F2.
My folder broke after 12k screenshots. To fix this, I copy/pasted every photo to another folder, then deleted the original ones. Now I can't open my recycle bin without my computer crashing. Use Gyazo .-.
using lightshot, gyazo, snipping tool, the f2 key all works. I take f2 screenshots then use gyazo to screenshot them which is weird but works well to me.