img = Import["https://i.sstatic.net/O14tf.jpg"] Using ImageMesh + BoundingRegion:
mindisk = BoundingRegion[ImageMesh[RemoveBackground@img], "MinDisk"] Disk[{56.0259, 59.0719}, 48.1942]
Disk[{56.0259, 59.0719}, 48.1942]
Show[img, Graphics[{FaceForm[], EdgeForm[{Red, Thick}], mindisk}]] 
img = Import["https://i.sstatic.net/O14tf.jpg"] Using ImageMesh + BoundingRegion:
mindisk = BoundingRegion[ImageMesh[RemoveBackground@img], "MinDisk"] Disk[{56.0259, 59.0719}, 48.1942]
Show[img, Graphics[{FaceForm[], EdgeForm[{Red, Thick}], mindisk}]]
img = Import["https://i.sstatic.net/O14tf.jpg"] Using ImageMesh + BoundingRegion:
mindisk = BoundingRegion[ImageMesh[RemoveBackground@img], "MinDisk"] Disk[{56.0259, 59.0719}, 48.1942]
Show[img, Graphics[{FaceForm[], EdgeForm[{Red, Thick}], mindisk}]]