Several tips for figure;

1. ticklable fontsize
set(gca, 'fontsize', 14)
can change the fontsize of a ticklable.
use get(gca) to get more information.

2.  title or text in several lines
title({'First line','Second Line'})
text(0.5,0.5,{'First line','Second Line'})

3. add lables to data points
for n = 0:N+1 
    figure;
    plot( (0:10:60), frame(:,n+1), 'b*-');
    axis([0 70 0 1]);xlabel('captured time. unit: min');
    ylabel('gray level');
    tmp = ['gray level', num2str(n)];
    title(tmp);
    text( (0:10:60) , frame(:,n+1)+.06,[num2str(frame(:,n+1))]);
    temp3 = ['C:\Data\Yang_Zmini\doc\graylevel_f',num2str(n),'.eps'];
    print('-depsc2', temp3);
end