Jābir ibn ‘Abdullāh (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) said: "When one of you betroths a woman, if he can look at what urges him to marry her, let him do so." So I proposed to a girl and would hide for her until I saw what urged me to marry her, so I married her.
This Hadīth indicates the desirability for a man to look at the woman whom he wants to marry. It is permissible to look at the face and the hands, for the face indicates beauty and the palms indicate plumpness or otherwise. This is the opinion adopted by most scholars. It is not required to seek the woman's consent to look at her. One may look when the woman is unaware of him, without knowing beforehand that he will look at her. In this respect, the Companion Jābir (may Allah be pleased with him) did so. If a man cannot look at the woman, he may send a woman whom he trusts to look at her and describe her to him. It is permissible to do this because it is more expected that the future spouses will live together amicably as their marriage was based on acquaintance, and so they would, most probably, not regret getting married to each other.