Using different images in content-single and content

Hello,

I’m trying to improve my site loading speed. I’ve noticed big images on my frontpage has a big impact on loading time. I’m using the_content() with more tag and for front page my theme has a boxy interface, so posts look smaller as well as the images I use in posts (check it from here).

So, what does browser do is loading 1200px wide image and resize it to 360px (for home page). My question is, how can I use different images for the part of the post seen on homepage before more tag and the single post pages?