I'm not too savvy on this, but I use Photobucket (PB) - free account - to host the images. There is an "Upload" screen on PB where you can drag and drop from any source. Once uploaded, go into your "Library" and click on an individual image. Beside each image to the right there is section called "Share Links" with URL coding that can be cut and pasted right into a post on here (use the bottom choice, marked "IMG" - click on the field and it will automatically put the code on your clipboard). Paste the code into your sale listing thread. As long as you don't mark your Photobucket folder "private" the image will show up in your post instead of the code that you pasted into your message.
PM me if you need more detail.
Paul