Colors> Reduce Colors in Design...
Photographic image uses many colors which is practically not possible to weave. The image needs to be processed so that the design has limited number of colors.
When you open an image (File>Open) with many colors, Galaincha software will give different options in the Used Colors palette, to process the design. You can also click on Colors> Reduce Colors in Design to reduce the number of colors.

Adjust the level of smoothness by Simplification and reduce the number of colors as per your requirement. This will automatically convert the image into specified number of colors. This is a very useful tool to convert any images into weavable design with fixed number of colors.

View tutorial on Processing a design by reducing colors