The code below can load a jpg and store it as matlab fig file.

So, this answers the question of how to convert jpg to fig file.

However, of course, the jpg stores only pixel information.

So, vector graphics (e.g., lines) are not drawn perfectly.

Good luck!

im = imread('Picture6.jpg');

fig1 = figure('color','w');

imagesc(im);

axis off;

saveas(fig1,'figure','fig');

Thank you all, your responses were helpful