Use a server like photobucket or flickr.
I can only explain flickr -
upload ur photos onto flickr.
Click on ur main photograph you want to upload.
To the bottom right is a sentence 'different sizes'
Click on this
Choose medium size
Copy the bottom ULR link
Enter clubsnap / your thread
Click on the icon with the mountian
paste the ULR
Finito!
Enjoy clubsnap!