A few ways:
The jpeg picture on your computer must be uploaded to one of two sources:
1. either use the Manage Attachments button at the bottom of the post or reply page and then follow the sequence or
2. chose a photo storage site that has links you can copy to this site.
Photobucket.com I find is the easiest. The photo link will be shown in a small box contained below the picture you've uploaded: [IMG]title of picture.jpeg [/IMG]. ( I upload pictures into different albums (IE lurecraft; scenic; family; club, etc.))
Copy [IMG] picture [/IMG] to the post and it will come up as large a picture as the original.
It's best to downsize the photo to no more than 5" on any one side so it doesn't take up a whole screen as well as being faster to upload.