Take screenshots with scrot (or tool specified in scrot-command),
upload them to imgbb and copy the url to the kill-ring.
Just call M-x scrot, select your filename (which is pre-filled
with a few suggestions. Use M-n to select different ones)
and then select the region you want a screenshot of.
If you call scrot with a prefix argument (e.g. C-u M-x scrot)
then the image will be inserted as an org-link in the current
buffer from where you called scrot.