Is this Icon of the Holy Spirit canonical?
The EO view is that it is not canonical. The Holy Spirit appeared as a dove at Christ's Baptism, but is not a dove by nature, so the dove imagery should only be used in icons of the Theophany, as it was, at that specific time and place, that the Holy Spirit manifested as a dove.
On the four creatures:
Imagery from the Book of Revelation of four mystical creatures (an angel, an ox, a lion, an eagle) in the presence of the throne of God were interpreted by the Fathers as mystically representing the four Evangelists: in order, Matthew, Mark, Luke and John. The following is Canon 82 of the Quinisext Ecumenical Council:In certain reproductions of venerable images, the Forerunner is pictured pointing to the lamb with his finger. This representation was adopted as a symbol of grace. It was a hidden figure of that true Lamb who is Christ our God, shown to us according to the Law. Having thus welcomed these ancient figures and shadows as symbols of the truth transmitted to the Church, we prefer today grace and truth themselves, as a fulfilment of the Law. Therefore, in order to expose to the sight of all, at least with the help of painting, that which is perfect, we decree that henceforth Christ our God be represented in His human form, and not in the form of the ancient lamb. We understand this to be the elevation of the humility of God the Word, and we are led to remembering His life in the flesh, His passion, His saving death and, thus, deliverance which took place for the world.
We also have, from his authoritative treatise In Defense of the Divine Images
, St John of Damascus’ statement of:Of old, God the incorporeal and uncircumscribed was not depicted at all. But now that God has appeared in the flesh and lived among men, I make an image of the God who can be seen. I do not worship matter, but I worship the Creator of matter, who for my sake became material, and deigned to dwell in matter, who, through matter, effected my salvation. I will not cease from venerating the matter through which my salvation has been effected.
Iconography is concerned with the fullness of divine revelation: in essence, the Word made flesh. Where only a prefigurative or mystical image has been revealed, then that image may be permitted in an icon. Where the fullness has been revealed (most notably in the incarnation of Christ), then only the fullness of that image may be properly depicted. As, according to Canon 82, it is not considered proper to represent Christ in His prefigured forms (as a lamb, as a youthful winged angel, etc), so also is it wrong to portray the mystical creatures in the book of Revelation with the inscriptions of the names of the Evangelists.
The Evangelists were human beings, and not the abovementioned creatures in essence or nature. Was St Mark an ox? Or St Luke a lion? Of course not. We should not confuse symbolic forms with reality. Therefore, while it is permissible to show these mystical creatures around the throne of God in icons of Christ in Majesty, as per the Book of Revelation, the inscriptions of the names of the Evangelist-saints should not be there.