It seems – and Allaah knows best – that this face, whether it is smiling or sad, does not come under the same ruling as images that it is forbidden to make, draw, or use, for two reasons: 

1 – It contains none of the features of a real face, such as eyes, mouth and nose, and it has no head or ears. 

The Prophet (peace and blessings of Allaah be upon him) said: “The image is the head; if the head is cut off, there is no image.” Narrated by al-Ismaa’eeli in his Mu’jam from the hadeeth of Ibn ‘Abbaas and classed as saheeh by al-Albaani in al-Silsilah al-Saheehah no. 1921 and in Saheeh al-Jaami’ no. 3864. 

2 – The majority of fuqaha’ are of the view that if something is cut off from an image without which it could no longer live, then it is not a haraam image. For a detailed discussion of this issue and the views of other madhhabs, see Ahkaam al-Tasweer fi’l-Fiqh al-Islami, pp. 224-240. 

But we should point out two things: 

This usage in chatting on the internet does not come under the drawing of images, rather it comes under the use of images. 

Please see the answer to question no. 78963. 

Secondly: A woman should not use these images when speaking to a man who is not her mahram, because these faces are used to express how she is feeling, so it is as if she is smiling, laughing, acting shy and so on, and a woman should not do that with a non-mahram man. 

It is only permissible for a woman to speak to men in cases of necessity, so long as that is in a public chat room and not in private correspondence. See question no. 34841. 

And Allaah knows best.