setProfilePicREST.js

var xhr = new XMLHttpRequest();

xhr.open("GET", "https://yoursite.sharepoint.com/sites/test/SiteAssets/imgToSetAsProfilePic.jpg", true);

xhr.responseType = "arraybuffer";

xhr.onload = function (event) {
  
  var imageAsArrayBuffer = xhr.response;
  
  if (imageAsArrayBuffer) {
  	    
    jQuery.ajax({
            url:_spPageContextInfo.webAbsoluteUrl + "/_api/SP.UserProfiles.PeopleManager/SetMyProfilePicture",
            type: "POST",
            data: imageAsArrayBuffer,
            processData: false,
            headers: {
                "accept": "application/json;odata=verbose",
                "X-RequestDigest": $("#__REQUESTDIGEST").val(),
                "content-length": imageAsArrayBuffer.byteLength
            },
            success: function (data) { 
                console.log(data);
                alert("profile pic set");
            },
            error: function (err) {
                console.log(err);
                alert("error");
            }
        });
  }
};

xhr.send(null);