T4rg3t5 discovers marker textures from the OpenMW VFS directory textures/s3/crosshair/. Add a DDS file there and select its filename stem through the TargetLockIcon setting.
Prepare the image
Use GIMP or another image editor to create a 128×128 marker with a transparent background. A clean black-and-white source works best because T4rg3t5 applies the configured health colors to the marker.
- Flatten the source to black and white. In GIMP, use Colors → Threshold and adjust the cutoff until the shape reads cleanly.
- Remove or lighten the black pixels. Colors → Levels can raise the black input level so the recoloring produces a useful result.
- Scale the image to 128×128 pixels.
- Export it as an uncompressed DDS without mipmaps.
Package and select it
Place the DDS in textures/s3/crosshair/. The filename stem becomes the setting value. The included marker uses the stem Starburst, so select it with TargetLockIcon = 'Starburst'; replace Starburst with the stem of your own file.
The settings menu enumerates VFS-visible DDS files in that directory. If the icon does not appear, check the package path, filename case, and DDS extension first.