This portrait was personally painted by Immortal Emperor Min Ren. It is not just a simple painting, but an Emperor's Possession and as such it serves as one of the Cleansing Incense Ancient Sect's Defining Treasures.
To prove that Su Yonghuang is the descendant of Immortal Emperor Min Ren, Li Qiye asked the elders to bring the Portrait. The elders compared the painting with Su Yonghuang, and discovered that they indeed had many similarities. Su Yonghuang then spilled a drop of blood on the Portrait. The blood summoned Immortal Emperor Min Ren's spirit from the painting and it looked at Su Yonghuang, confirming her status.
Next day Li Qiye lead a group of Sect's members to the Evil Infested Ridge. Elder Gu Tieshou brought the Portrait with them for protection. Shortly after they arrived, Li Qiye ordered Gu Tieshou to use the Portrait to deal with all enemies once and for all.
As an Emperor's Possession, the portrait contains a limited ammount of Immortal Emperor Min Ren's power and immortal spirit. It can be used to expel powerful enemies, but unless it is a sect-destroying calamity, the Cleansing Incense Ancient Sect would not easily utilize it.