set terminal png set output "plot.roc.png" set key right bottom box 3 plot 'roc1.txt' using 2:3 with lines lw 2 title "MOPS + SSD", \ 'roc2.txt' using 2:3 with lines lw 2 title "MOPS + ratio test", \ 'roc1.sift.txt' using 2:3 with lines lw 2 title "SIFT + SSD", \ 'roc2.sift.txt' using 2:3 with lines lw 2 title "SIFT + ratio test"