I wouldn't try to fix your image sizes using code, because it seems like your images are massive.
If you design an image at 1440px x 900px, & your monitor size is 1440 x 900px, then that's how big the image is in size, not resolution. A smaller screen will then try to see that width of 1440px within it's window of only 800px.
You need to resize your original images to fit within smaller screens.
Resolution is all about the size of the pixels themselves, but a 700px image is still a 700px image, no matter what size resolution or screen size you are looking at it from.
Simply put, the image size needs to be matched to your target users computer resolution. eg. if only 2 of your users have huge monitors with high resolution, then they are the only ones that will be able to benefit from your images at the current target size on their screens.
If you want to have a wider audience, you need to design the original images in say 800x600 or 1024x768, because more screens will be able to show the entire image on the screen.
Please note: Image size is not the same as Image resolution. You can have a 300dpi image and a 150dpi image and they can both still be 700px wide. More dots per inch(dpi), will only enhance the quality(and file size) in most cases, but most older screens are still going to show the image the same size.
Just to let you know, the older screens are 72dpi and some newer ones probably go up higher to 96dpi (I think I've seen this on an LCD windows setting) - so if you make your images higher than say 100dpi, it's just a tax on filesize. If you are designing for print, then that's a different story...
Hope this helps,