Clark Ashton Smith (CAS) described the origin of this poem in a letter* to August Derleth from January 1944:
Here's my first poem of the year. It was suggested by a photo of herself that Lilith Lorraine sent me.
Lilith Lorraine was a literary pseudonym for Mary Maude Dunn Wright, a woman of many talents who wrote fantastic poetry, and was a mutual admirer of CAS' work. The Bard of Auburn also wrote an introduction to Lorraine's poetry collection A Wine of Wonder (1951). The text of that introduction is available on The Eldritch Dark:
As a tribute to a fellow poet, "Lines on A Picture" is quite heartfelt, and CAS beautifully captures the unique qualities of a writer steeped in the supernatural and the weird:
Perchance your mouth is strangely wistful
For hidden things you know not of:
Your eyes forget, your lips remember
Some lost and Atlantean love.
It's hard to imagine higher praise from CAS than the opening line "O face upturned to alien splendors!" It seems clear that CAS had found a kindred poetic spirit in Lilith Lorraine, and it's quite moving to read his lyric tribute to her.
*See letter #311 in Eccentric, Impractical Devils: The Letters of August Derleth and Clark Ashton Smith published by Hippocampus Press.