You can do a search in the forum.
Short answer; pick a third party hosting site and upload your jpg files to it.
Most of us use sites like postimage, imgur. I prefer the sites that charge a nominal fee in return for not having links to Russian girls who want to meet you. In my case Fotki.
On that site open the window which will identify the web address of your image. Copy that.
Open the compose window on FSM forum.
Type your reply and position the cursor where you want the photo to show up.
Click on the insert/edit image button, the one that looks like a mountain.
Paste the image url you copied from your sharing site into the source window.
Your image link will show up as the actual image, but it is the link to your share site.
Bill