It is a photo of a Flameskull, a tiny undead neutral evil. Blazing green flames and mad, echoing laughter, follows a disembodied skull as it patrols its demesne. When discovering tresspassers it blasts intruders with fiery rays from its eyes and dreadful spells called up from the dark recesses of its memory.

From the D&D Monster Manual, p134.

https://5e.tools/bestiary.html#flameskull_mm,fbsr:flameskull