Here is a link to the Documentation on using Media Items API.
http://wiki.developer.myspace.com/index.php?title=OpenSocial_0.9_MediaItems
It explains how to use it.
you need to Issue a POST request on following URL
http://api.myspace.com/1.0/mediaItems/{personId}/{selector}/@videos
if its image then set content-type to image/{type} like content-type="image/jpg"
for jpg
these formats are supported: .jpg, .gif, .bmp, .tiff, .png.
similarly for videos use content type like content-type=”video/mpeg”
these formats are supported .avi,.mov,.mpg,.wmv.
For more details please consider checking out above link.
For details on what a POST request is or what is its structure check out this http://www.jmarshall.com/easy/http/