HI Usha,
There are two ways to do it.
If you are copying the picture from the internet, then Click on :
And enter the URL .
If you are going to take a picture saved on your computer then :
Scroll down below the text box and you will find the button " Manage attachements" . Click on that button and you can upload any picture as long as it conforms to the size limits.
Click the preview button the page before submiting, so you can fix any errors before posting the blog.
Hope this helps.
Vandhana