Here is the code:
Using an image of your own or one hosted from an outside website will work either way. Simply upload the image or copy and paste the site where the image is being hosted. Click on HTML at the top left while in compose mode of your Google Blog post and enter <marquee></marquee>.
Next while your mouse courser is in between <marquee></marquee> click on the image icon and choose one of the options below to upload your image to your Blog.
Add an image from your computer
Add another imageWe accept jpg, gif, bmp and png images, 8 MB maximum size
Or add an image from the web
Add another image
Learn more about using web images