snagit is a paid one isn't it?
For free (Windows) you can use CTRL+PRINTSCREEN then paste the image into Paint and crop as needed.
Snipping Tool in Windows is even better/easier.
But you still need some online service where to upload picture first, correct?
Yes you have to upload it online..... it will not do it automatically. Unless you had like a google drive or dropbox it sends to automatically.
There are multiple image sites listed in here you can upload to.