An image or document can be added through the 'attachments and other options' link on the posting page.
There is a maximum size of 128KB. This may get you up to ten pages on a Word document but only a couple on a .pdf, depending on the formatting.
Photos will have to be reduced in size, say to 800x600px in photoshop then using the 'save to web' option to reduce the number of KB further.
A quick way to reduce size is to email the photos to yourself using picasa. I gave out illustrated instructions when visiting the class groups. (too large to attach!)
Although you can read some of the posts without logging in, you do have to log in to read the attached documents.