When in doubt always look for errors: Disregarding the jaggies, parts of backpack including the anchor are clipping through the skirt. Skirt itself has some awkward lines too. That's a direct evidence of 3D.
Indirectly you can infer the artist's traditional skills are not up to the level of detail offered by CG. Lighting is inconsistent. Source used in the 3D scene was positioned differently than the big old flash, which was added later. It's especially visible on the face and left hand which are mostly shaded when they should have been lit. You can even trace the light's path back to the original source. It was way out of the frame to the upper right, so far away that rays in the picture are nearly parallel. That's incompatible with having an intense flash so close.
The navigation lights(?) on the mast are only suggested by use of simplistic halos. No proper reflections visible on the rig. Poor water in general, and reflection of the flash visible on its surface is just a featureless blot; Wrongly positioned too.
Compared to the previously posted picture, lines and straps visible around the rigging remain in exactly the same positions. Same for the wind indicator. When drawn manually flexible objects like these are generally adjusted to fit their positioning in space. It's a model.
Overall it's not a bad picture, but it can't pass for something expertly painted by hand. Retouched 3DCG without a doubt. Tag it so.
For shows like Kantai Collection, they tended to do machines with CG, since CG has all those hard edges that are obvious on human characters, but less so on a tank or ship parts, while CG can also keep all the details accurate and consistent.
In the anime, they'd do really obvious things like have Naka be hand-drawn, but her armament be CG, which created obvious clashes.
In this case, it's all CG except the obviously dissonant background (look at the waves), the posing is a bit stiff (see the left arm), which is a telltale sign of hand-posed models.
