When you are logged in flickr, you can access your images because you have entered a username and password.
InLinkz does not have any access to your password of course, and because of this, it cannot access what you see.
So , you need to be logged out of your account and your picture to be public in order to add it to a linkup.
To do so, just log out of flickr and check your photostream.
Then, click on the picture you want to add:
And copy the URL as usual, adding it to the linkup tool
Your image will be available as the first one.
You will notice there is a small separator underneath the first image. This actually separates the big images (like the one you want to add) from the thumbnails that reside on the side bar.
Don’t forget that if you want the same image added in another linkup, you can use the “Show history” button at the top right of the page!