metaWeblog.newMediaObject (blogid, username, password, struct) returns struct

The blogid, username and password params are as in the Blogger API. 

The struct must contain at least three elements, name, type and bits.

name is a string, it may be used to determine the name of the file that stores the object, or to display it in a list of objects. It determines how the weblog refers to the object. If the name is the same as an existing object stored in the weblog, it may replace the existing object.

type is a string, it indicates the type of the object, it's a standard MIME type, like audio/mpeg or image/jpeg or video/quicktime. 

bits is a base64-encoded binary value containing the content of the object.