You have two options as listed bellow:
#1 - For users using Flickr.com you want to use the HTML/BBCode.
For users using Photobucket.com you want to use the [IMG] Code.
& if you do not know how to find those follow what is show bellow.
#2 - go to FLICKR find the photo you want to post
when you did, simply right click the picture and click on
"copy image location"
and then follow what is said on the picture bellow
just click send and your all done!