How does image data work for group of images (more than one images)?

Questions
,
1

Consider the following code:

list = Map[Import,{"img.png"},{"img1.png"}];
    Transpose[Imagedata[list]];

It is shows error. But if I apply,

Import["img.png"];
Transpose[ImageData[%]];

for one image is worked perfectly. Can anyone help me to solve this problem.