Classifieds are the For Sale sections.
In those sections you can simply upload upto 3 images per message from your computer.
There's a section below the text box called File Attachments.
In all the other sections, the pic must already be hosted somewhere on the internet, & you use the "artwork" icon above the textbox to insert a link to it.
When uploading pix, check the size of them at 100%. ie not zoomed in or out. It gets annoying to have photos bigger than the normal screen show up & then having to scroll across to get to the Prview, spell-check, reply, edit, etc buttons.
Plus it takes longer for the page to open.