Jim,
You are posting a thumb nail.
When you log in to Photo bucket click on the album you uploaded the picture to.
When the album opens, move you cursor over the picture you want to post and a menu will pop down.
Move you cursor down to the box next IMG Code and click on it. The box will turn blue. With your cursor arrow still on the blue highlighted text, right click you mouse and select copy.
Nove to the reply window, left click you mouse to put the curor in the reply window. Right click and paste. The coded text wil appear.
If you still get a thumbnail it may be because you are uploadiong a thumbnail. You wil have figure out that part on you computer.
Try that and I will tell you have to resize pictures in photo time in another posts.