I'm writing this as I do it:
Click "Additional Options" to the lower left of the text area.
On the "Attach" line, type in your file name (as if), or click the "Browse" button.
Select a picture (don't accidentally browse in your porn collection -- this is a family-friendly site!).
If you want to put in two pictures, click the "more attachments" link, just to the right of the Browse button
Find another (clean) picture.
When you're done adding pictures, click "post".