For a muslim woman who post her picture on social media pages and groups is haraam for a number of reasons. Add to that the woman is not properly dressed or covered and the parts of her awra are visible in the photograph than that manifolds the sin and makes it, even more, worse and prohibition more emphatic.
When a person likes something he is in a way approving of what he has liked. In simple words liking what is published on a persons social media account is kind of approving of what they do and at the very least the one who put up the picture will understand it as such, especially if the one who adds the like is a knowledgeable or religiously committed person or one who appears outwardly to be righteous and committed.
The Prophet (blessings and peace of Allah be upon him) said: “Whoever among you sees an evil action, then let him change it with his hand [by taking action]; if he cannot, then with his tongue [by speaking out]; and if he cannot, then with his heart – and that is the weakest of faith.”
Abu Dawood narrated in his Sunan (4345) from al-‘Urs ibn ‘Ameerah al-Kindi that the Prophet (blessings and peace of Allah be upon him) said: “If sin is committed on earth, the one who sees it and hates it – or denounces it – is like one who was absent from it, and the one who is absent from it but approves of it is like one who sees it.”
Classed as hasan by al-Albaani in Saheeh al-Jaami‘, no. 689; it was also narrated in a mursal report.
Ibn Rajab al-Hanbali said: The one who witnesses a sin and hates it in his heart is like the one who did not see it, if he is unable to denounce it or change it verbally or by taking action. The one who is not present when it happens but approves of it is the one who saw it and was able to denounce it or change it but did not do so. That is because approval of sins is one of the most abhorrent of forbidden matters, by which one fails to denounce the sin in one’s heart, which is obligatory for every Muslim and this is not waived for anybody under any circumstances whatsoever.
End quote from Jaami‘ al-‘Uloom wa’l-Hukam(2/245)
Hence even in liking anything on social media one must be very cautious. It is not only about liking a picture improperly dressed woman but anything that is not acceptable in Islam. Our each and every action matters and will be held accountable.
If a person adds a “like” for any of these pictures or the like, what expression of objection has he made towards the evil action that has been committed? None! Instead, he has accepted it and approved it and deemed it right.
And Allah knows best.