Is watching pornography a sin?

The term pornography is defined as writing about prostitutes. Pornography has progressed from pictures to videos. This is a composite word formed from the Greek words porne (prostitute) and graphein (writing). The term "prostitute" also refers to someone who exploits their talents or compromises their self-esteem for personal or financial gain. 

Porneia is translated in Scripture as "marital unfaithfulness," "fornication," and "sexual immorality." As a result, anyone who engages in pornography is committing sexual sins in her heart, which grieves the Holy Spirit.  

For this is the will of God, your sanctification: that you abstain from sexual immorality (Gk porneia); that each one of you know how to control his own body in holiness and honor, not in the passion of lust like the Gentiles who do not know God; that no one transgress and wrong his brother in this matter, because the Lord is an avenger in all these things, as we told you beforehand and solemnly warned you. For God has not called us for impurity, but in holiness. 1 Thessalonians 4:3-7