You can attach files (including images) to the call sheet.  These files are sent as attachments to the email when you publish the call sheet and are accessible from the mobile view of the call sheet as well.

To attach files to the call sheet, visit the "Attachments" tab of the call sheet builder.

Here you can add file(s) by dragging them into the gray zone or by clicking on the gray zone and then selecting the file(s) that you wish to upload.  You can also remove existing attachments from this page.