In order that all parts of your thread have the same archival durability, the attachments feature of vBulletin should be used.
Expanded from the FAQ:
This forum uses the attachment feature of vBulletin to give you the ability to attach files of certain types to your posts. This could be an image, a text document, a zip file etc.
Pictures which you upload must not exceed 1280 pixels in width, 1280 pixels in height or a file size of 1mb if they are not to be rejected. Please refer to this thread
for fellow member's suggestions about free programs allowing you to resize and compress pictures. You may include up to 12 attachments per posting, and may reply to your own thread if more photos are needed.
When you are making a reply or a new post, there will be a box lower on the page entitled "Additional Options." Click the "Manage Attachments" button within that box to bring up a window where you may indicate the pictures you wish to upload.
To attach a file to a new post, simply click the top [Browse] button at the bottom of the post composition page, and locate the file that you want to attach from your local hard drive. Additional windows with browse buttons are included so that you may attach multiple images in a single pass. When you are done, click the "Upload" button in the box and wait until the images are uploaded. Then you may close the window and proceed with your post.
Only certain types of files may be attached: these are the valid file extensions for files to be attached to this forum: bmp doc gif jpe jpeg jpg pdf png txt zip.
After posting, the photos will appear in a group at the bottom of your post in the same order as they were entered.