Sending PHP the retval of the Object URL created from an image (blob:http://...) and using PHP's base64_encode() along side with file_get_contents() returns an error claiming that there is no stream or file.
How about send url of image. then use file_get_contents('http://...') to get the image file content.
For example, your image url is http://example.com/test.jpg
JS
// if image is a link
axiso.post(url, {image: "http://example.com/test.jpg"})
// if image is file select from local, upload file
let data = new FormaData();
formData.append("image", this.files[0]);
axiso.post(url, data, {headers: {'Content-Type': 'multipart/form-data'}})
PHP
// get file content from image link
file_get_contents('http://example.com/test.jpg')
// get content from upload file
$name= "image";
file_get_contents($_FILES[$name]);