How to draw lines in between points that the user provides?

I have a picture uploaded to matlab where I have the user pick four points, then I shall have red lines that are made in between those points that should make a square (or somehat close to a square). I also what to convert the image to grayscale using the 'jet' colormap. This is my code so far:

The x = ... and y = ... is clearly wrong as it makes a seperate figure with lines and the lines are not on the picture.

clc;    
close all;  
clear;  

%%
davis = imread('DavisHall.jpg');
figure(1), imagesc(davis), axis image
PickCorners = ginput(4)

x = [PickCorners(:,1)];
y = [PickCorners(:,2)];
plot(x',y')

hold on

davisgray = rgb2gray(davis)

Answer 1

[Adam Danz]

"The x = ... and y = ... is clearly wrong as it makes a seperate figure with lines and the lines are not on the picture. "

You need to specify the axis in your call to plot(). After calling imagesc() get the handle to you axis using gca()

h = gca;
hold(h, 'on')
plot(h, x', y')

If you want to draw a square, you'll need to add the first coordinate on to the end of each x and y vector to complete the square.

plot(h, [x;x(1)]', [y;y(1)]')