Convert data:image/png;base64,iVBORw0KGgoAAA to []byte

go

func streamToByte(stream io.Reader) []byte {
	buf := new(bytes.Buffer)
	buf.ReadFrom(stream)
	return buf.Bytes()
}

// pass reader to NewDecoder
dec := base64.NewDecoder(base64.StdEncoding, strings.NewReader(base64string[i+1:]))