Woman riding with a non-mahram man

With regard to clothes on which there are pictures, it is
haraam to wear them for adults and children, males and females, alike. 

See Question no.
10439. 

With regard to a woman riding with a non-mahram man, one of
the following two scenarios must apply. 

1 – That she is riding on her own with him. This is the
khulwah (being alone with a member of the opposite sex) which is forbidden.
The Prophet (peace and blessings of Allaah be upon him) forbade it when
he said: “No man is alone with a (non-mahram) woman but the Shaytaan is the
third one present.” (Narrated by Ahmad and al-Tirmidhi in his Sunan,
2092; also in Saheeh al-Jaami’, 2546). See also question no,
2986. 

2 – That she is riding with a group of women and that
non-mahram man. This is permitted, subject to two conditions:

(i)That the man should be
trustworthy

(ii)That it should not be a
journey, rather it should be inside the city. But if that is a lengthy
journey then it is haraam for her to travel without a mahram, because the
Prophet (peace and blessings of Allaah be upon him) said: “It is not
permissible for a Muslim woman to travel the distance of one night’s travel
without a man who is her mahram.” (Narrated by al-Bukhaari, 1088; Muslim,
1339. This version narrated by Muslim).

Based on that, it is permissible for a woman to ride with her
sister’s husband if they are accompanied by her sister, and it is
permissible for her to ride with her husband’s brother if they are
accompanied by his mother, if there is no danger of fitnah.