To post pictures in the thread look in the Additional Options" panel below the main "Thread" text panel.
The first two "Miscellaneous Options" should be checked which will allow you to embed media from hosted sites (like YouTube etc...NOTE: some sites protect their hosted media from being embedded to other servers/sources).
The second portion of the panel, "Attach Files," allows direct attachment of photos that meet the size limitation criteria (they can't be too big or the data would start to slow down the forum). This method allows the VDF to store a copy of the image for future reference (especially useful for posting pics and descriptions from eBay and CL or if the image gets "unhosted" from the original source -- for historical and market purposes).
Click "Manage Attachments" and choose an upload option. Some hosting sites have protection (or additional digitial rights managment) on media / photos and will not display the images if you choose "Upload from a URL," in that case simply choose the "Browse" option and navigate to where the photo resides on your computer, left click the image file to highlight it and select "Open" or just double-click to insert the file path in the "Upload File from your Computer" text box, then click "Upload."
The "Attachment Key" will provide information on the maximum file sizes that can be uploaded. Any upload errors will be displayed in the "Manage Attachment" panel.
"Preview" your final post before submitting, then select "Submit" when ready to post.