Dead center fastest any easiest way to get there

[iDad]

tips any one have a tip? I have 33 pictures all needing dead center marked with a small tranparent square whats the fastest way to find it most pictures are all different sizes

 

[SCTRWD]

Add a square layer: Fill opacity - 0, Knock out - Deep.
Select All. Layer->Allign Layers to Selection->Vertical Centers. And Layer->Allign Layers to Selection->Horizontal Centers.

 

[Gaussian]

Make an action for that and apply it to all using Automate --> Batch