Jim, when you are looking at your photo gallery in flikr, click on the photo you want to post. Then you have two options. One option is to right click and choose a size, I usually choose the largest medium size. After you have clicked on the size you want, it will take you to that size. Then right click on that image again and select, "copy image location". The other option is after you have clicked on the photo you want, there is a drop down menu at the top left of the picture. Select "view all sizes". It will usually default to the large size. You can choose another size if you want. When you have the size you want, then right click and select "copy image location". Then when you are writing a post, click on the "enter an image" icon and choose what type of floating image you want, then hit "Ctrl-V" to past the image location.

Hopefully that will help. I use flickr as well.