The Flickr API expects all data to be UTF-8 encoded.

Checks are made for valid UTF-8 sequences. If an invalid sequence is found, the data is presumed to be ISO-8859-1 and converted accordingly to UTF-8.

Sending data in any other encoding will result in garbage into Flickr. It wont be dangerous garbage (we will always store valid UTF-8) but it will still be garbage.

More information about UTF-8