If you are keeping all the 1000 images in the res folder, the application size will increase by 2-4 Mb.
So, better go for downloading images from web server using lazy loading. Because, usually users won't scroll down to more that 100 items. So to show <100 images for 99% of the time, its useless to have all the 1000 images in the application res folder.
Check the highest voted answer here:
Lazy load of images in ListView
Thats what i am using in my application. Very happy with it.