The ornamental design for semi-panel image for a cap, as shown and described.
FIG. 1 is a rear perspective view of semi-panel image for a cap showing my new design;
FIG. 2 is a rear elevational view of FIG. 1;
FIG. 3 is a reduced right side elevational view of FIG. 1: the left side is a mirror image; and,
FIG. 4 is a reduced top plan view of FIG. 1.
The broken line showing of a part of the crown and the visor is for illustrative purposes only and forms no part of the claimed design, and the broken line shown in the solid line on the part of the crown represents stitching.