Content Type not being set

I've tried many things after reading the documentation on how to set the content type, and nothing works.

// var options = { contentSettings: { contentType: 'image/png'}};
var options = { contentType: 'image/png'};
blobService.createBlockBlobFromLocalFile(blockBlobContainerName, blockBlobName, imageToUpload, options, function (error) {
...

Neither one of the options choices above will set the content type for the file. In this case it's just an image, either a .png or .jpg.

Please tell me how to get this to work.