Shabbat 149 - How to count guests and read cartoons on Shabbat

One can count his invited guests, to know how many loaves of bread he will need, and the deserts he will serve - if he does it orally, but he should not read them from a written note. Why? Because he might come to erase someone from the list, and erasing is prohibited on Shabbat. Another reason is that he might get accustomed to it and start reading business documentation. Some forbid even reading social correspondence.

What practical difference is there between the two reasons, erasing on Shabbat and reading business documentation? If the writing is very high on the wall, he will not come to erase it there. 

Can one read captions under a picture? Not on Shabbat! And the picture itself is forbidden to look at, even on a weekday. Why? Because of "do not turn to idols" which are born of your imagination. Some say that a cursory look is allowed, and others that it refers only to idols that were prepared but never worshiped.

Art: Girl Reading a Letter at an Open Window by Johannes Vermeer