Download the zipped files from the archival links below which contain the codes for the methods of, respectively, Tan and Ikeuchi¹, Shen et al.², and Shen and Zheng³. Then, place the therein contained images inside this folder. See structure below.

Note: the links were archived directly from the respective authors' pages (see link suffix) where their codes along with test images are freely distributed for research purposes.

¹ http://web.archive.org/web/20190828202158/https://tanrobby.github.io/code/highlight.zip
² http://web.archive.org/web/20190828202109/http://ivlab.org/publications/PR2008_code.zip
³ http://web.archive.org/web/20190828202133/http://ivlab.org/publications/AO2013_code.zip

The images folder should have the following structure.

README.md
animals.bmp
animals_gt.bmp
cups.bmp
cups_gt.bmp
fish.ppm
fruit.bmp
fruit_gt.bmp
head.ppm
lady.bmp
masks.bmp
masks_gt.bmp
rabbit.bmp
toys.ppm
train.bmp
watermelon.bmp
wood.bmp