CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. It is used for prevention of automated script from spammers. Normally it contains some random alphabets and number in image. User has to write same in text box provided.
Simplest way to upload file is by using FormData. It is used in key/value pairs to send XMLHttpRequest. Initially FormData used to send all form elements data in key/value pair, but it can be used to send keyed data also. Data sent by FormData is in same format as used in form's submit() method. It sends upload data also, if we use multipart/form-data in form's encoding