Content-Type: application/octet-stream
Content-Disposition: attachment; filename="picture.png"
Means "I don‘t know what the hell this is. Please save it as a file, preferably named picture.png".
Content-Type: image/png
Content-Disposition: attachment; filename="picture.png"
Means "This is a PNG image. Please save it as a file, preferably named picture.png".
Content-Type: image/png
Content-Disposition: inline; filename="picture.png"
Means "This is a PNG image. Please display it unless you don‘t know how to display PNG images. Otherwise, or if the user chooses to save it, we recommend the name picture.png for the file you save it as".
原文：http://www.cnblogs.com/allonkwok/p/5555698.html