I could not have imaged there would be joy in this. (Para. 3)
Meaning: In the very beginning, I didn't see in my mind or picture that there would be joy in the job.
Please notice the subjunctive mood used in the sentence.
image: vt. make a copy of the form of something; make picture of; see in the mind
Try to image being on the moon. 设想一下在月球上会是怎么个样子。
Can you image a world without wars and fighting? 你能设想一个没有战争、没有冲突的世界吗？
It is hard to image a society without law. 很难设想一个没有法律的社会会是个什么样子。
image: n. a copy of object(s); mental picture of an object
I cannot make an image of that old novel in my mind. 这本小说在我脑海里的印象已不深了。
He is the very imag of his father. 他的长相酷似他父亲。