The signature of the recommendation letter cannot be uploaded. Please ask the teacher to print it out and sign it in person before sending it to the subject. Although it is a lot of trouble, this is the safest way. Although most colleges may not be too strict in this regard, if you are unlucky and the school feels something is not right, you may be in trouble. Although the questioner must have said hello to the teacher, this will definitely leave a bad impression on the other school.