Downloading the image files separately as well
I think this command could get you started.
wget -r -P /save/location -A jpeg,jpg,bmp,gif,png http://textbook.s-anand.net/ncert/class-xii/chemistry/hello-this-first-chapter
It allows you to specify the location to save the images and which types of files you wants. Maybe downloading the images as such is easier.
Source:
-r enables recursive retrieval. See Recursive Download for more information.
-P sets the directory prefix where all files and directories are saved to.
-A sets a whitelist for retrieving only certain file types. Strings and patterns are accepted, and both can be used in a comma separated list (as seen above). See Types of Files for more information.
Copying the image files from your folder
I have noticed that the website uses PNG image files. You can just copy those from your folder. This should be run in the folder where you stored the webpage.
find . -name "*.png" -exec cp '{}' ./some_dir/somewhere/ \;