All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Drawing living objects is strictly prohibited in Islam because many Ahadeeth prohibit us from doing so. Ibn Mas'ood reported that the Prophet, sallallaahu 'alayhi was sallam, said: "Those who will receive the most severe punishment from Allaah on the Day of resurrection will be those who depict living objects." [Al-Bukhari and Muslim]
In another Hadeeth, the Prophet said: "Those who depict images will be punished on the day of resurrection; it will be said to them: 'Breathe a soul into what you have depicted.'" [Al-Bukhari and Muslim]
Besides, Ibn 'Abbaas narrated that the Prophet said: "Every depicter will go to Hell and for every image he has made, there will be appointed one who will chastise him in Hell." [Muslim]
These Ahadeeth and many others show that depicting living objects is strictly prohibited. However, depicting the head only without the body is a matter of controversy among the Muslim scholars. Is it also forbidden as the above-mentioned case? The predominant opinion of the majority of the Muslim scholars is that it is not prohibited. Al-Ramli, may have mercy upon him, who is a Shaafi'i scholar, said: "As for depicting the whole body without the head, the scholars have different opinions about this, though the predominant opinion is that it is forbidden." Indeed, this last view is the safest opinion. The Prophet said: "Leave that about which you have doubt and adopt that which you are certain of." [An-Nasaa'i]
In another Hadeeth, the Prophet said: "Whoever avoids doubtful matters, safeguards his religion and honour, but he who engages in doubtful matters, eventually falls into prohibitions." [Muslim]
If this is the case, then it is best not to use or exchange via email the kind of images you are asking about. If using or exchanging these pictures is forbidden, then the least you can do is to reject this evil within your heart. When you use or exchange these images, you are doing something that contradicts the above mentioned rejection by one's heart.
On the other hand, if using these images is not forbidden, they remain doubtful things, about which the Muslim scholars are not decisive, and it is better to avoid doubtful matters as mentioned in the Hadeeth, "Whoever avoids doubtful matters, safeguards his religion and honour."
Allaah Knows best.