同学你好，该知识点来自沪江网校《英语零基础直达大学六级【全额奖学金班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
that was drawn是多余的，the painting本身就是“画”的意思，不需要说the painting that was drawn画的画，意思重复。
这句话可以说
This painting is said to be Picasso's masterpiece.
The painting is said to be a masterpiece by Picasso.

by sb一般放在作品之后，比如
a play by Ibsen 易卜生写的剧本

be动词的时态要根据语境判断，如果这是一个现在的常态，直接用一般现在时就可以了。

祝同学学习进步~