Answer 1

just upload the image to some free image storage service like https://imgbb.com and attach a link to it (add a small comment if needed)
the SL staff goes over the lesson before publishing and makes final edits
if the image is relevant it will be most likely uploaded and to SL server and attached in the lesson

Answer 2

1. No need to delete the thread, it's complete On-Topic because it's about SL.
2. The images have to be on Sololearn's server to add them.
This thread by Swapnil can answer you better. See the answer marked as "Best Answer" there.
https://www.sololearn.com/discuss/881140/?ref=app