Well, images is one of WP's weak points.
First of all - stop uploading full sized images in first place, by that I mean photos from your camera, downloaded/self created artwork, high resolution, MB-heavy Photoshop creations etc..
My personal experience is that people mostly don't think about image size when uploading stuff to WordPress - but you have to - before uploading. Raw images from a camera, even a mobile phone can easily have 5-10 MB per image.
Unless your WordPress installation is expertly tuned to handle big images like a pro,
your WordPress installation will soon slow down and become huge.
Before you upload them, it is absolutely necessary to shrink images in size, with a tool (Photoshop, Gimp, etc.) (Sure, there are hundrets of plugins within the directory, some good, some bad).
To track down the issue, you can do several things:
install "registered image sizes". This plugin will list all "registered images sizes" within WordPress and show you the available formats.
go to "settings > media" and have a look at the default settings. You may want to shrink down the largest image size to maybe 1024 x 768 or something like that.
after that, download and install "regenerate thumbnails". This plugin does a fairly good job of re-creating your thumbnails with an optimized size.
You can also register your own image size within your functions.php and use that specific image size in your frontpage. See Codex: Add Image Size.
Additional info: you can enter "0" within "settings > media sizes" (small, medium, large) in order to prevent WordPress from creating dozens of different image sizes.
As far as I know, the cropping option doesn't make any difference in this matter.
Also consider cleaning up your database with something like wp optimize, or database cleaner. WordPress saves every tiny little thing and bloats the database by default.
Lastly I'd recommend using a caching plugin in order to speed things up.
WordPress Fastest Cache is the tool of my choice in this matter.
It makes your loading process reallllly faster.
- only upload optimized images in first place
- optimize the image output (either by plugin or by yourself)
- use a caching plugin to speed things up