Below is a write up from Grainger's FAQ, but here is how I do it:
1. Upload picture to a hosting services somewhere (e.g., Flickr or whatever)
2. Right click on picture and select "Copy Shortcut". (Alternatively, you can right click, select "Properties" and then copy the address/URL)
3. Go to the Bottlehead page and start a new topic
4. Click on the picture of the Mona Lisa in the tool bar. For me, this is right under the big "B" for bolding text.
5. Paste the URL to the picture inbetween the "[i-m-g]" and the "[/i-m-g]" (ignore the hyphens, I have to put those in or the system thinks I'm linking to a picture)
6. Finish your writeup and click "Post"
FWIW, I have had greater success when the picture I'm linking to is less than 1,000 (or possibly 900) pixels wide.
This is from Grainger's FAQ:
7. Q: How do I post a picture in a Bottlehead post?
A: There are two ways. The first is to write your post and then use the Preview key under the posting window. Next, select Additional Options... and Attach: then attach pictures from your computer. There are size limitations and a limit of 4 pictures in any single post.
The other way is to host your pictures somewhere. I use Photobucket. It doesn't cost anything.
For example, on Photobucket when I look into one of my albums and put my cursor on the picture I want to post. To the right is a list that says, "Image Links". You click on "Direct Link". Clicking on it once saves the direct link to memory like a Copy command does. Another way is to look at the picture full sized and move the cursor onto it. Right click and select "Save Image Location."
Compose your post. Hit Preview and where you want to insert the picture click once. The Insert Picture hot key is directly below the Bold hot key. When you click on it the cursor will be positioned between a pair of brackets. Don't move it but right click and choose paste. That inserts the hosted URL between the brackets.