Use a geometric distortion correction rather than a simple crop. Since the scan is slightly curved/warped, you’ll want to de-skew or apply a warp/distortion transform to map the bent edges back to a true rectangle.

One tool specifically mentioned for this is ImageMagick, which can handle complex image distortions from the command line. Its distortion features are commonly used to straighten scans, correct skew, and fix curved or radial warping.

In general, the right approach is:

• correct basic skew/perspective first if needed
• use a warp/distortion tool for the curved edges
• fine-tune until the photo’s sides align to a rectangular frame

If the distortion is more like bowing or lens-type curvature, look for circular or radial distortion correction methods. Those are designed for this kind of non-linear edge bending.