Upload image to Blogger host
Although there are many Image hosting sites like Photobucket & TinyPic but its better that you use your very own Blogger to upload the desired image.
To upload blogger image follow these steps.
1- Log in to your Blogger account click New Post button to create a new post.
2- In the new post click the image icon and add an image to display in the post
3- Once your image is uploaded,switch to HTML from compose.
4. Find the following code
http://2.bp.blogspot.com/-tnS4EzYUrnM/UI67LG_PxGI/AAAAAAAACKk/P-9VNnaloFQ/s1600/nby617ipyi.jpg
The above code tells where your image is saved in the blogger.You can use it in blogger posts as backgrounds.