The practical answer is that you can’t fully prevent access to your image files if you hand them to a print shop. If you need absolute control, print them yourself with your own printer and paper.

Otherwise, the best protection is to use a reputable lab or local shop with a strong reputation. A business that depends on repeat customers is unlikely to risk legal trouble and damage to its credibility by misusing customer images.

Before printing, make sure your files are prepared properly for the print size you want, and understand that color/paper handling can affect results. If you print at home, using the printer maker’s recommended paper often gives decent results even without advanced calibration.

So, in short:

• Absolute control: print at home.
• Best practical safeguard at a shop: choose a trustworthy, well-reviewed printer.
• If something improper did happen, legal remedies may exist, but prevention mainly comes down to selecting a reliable business.