How large are your image files (file size)? Uploading images with very large file sizes will take far more time, and will severely slow down your site.
1. Uploaded image dimensions: no more than 1000px wide (most monitors in use today are 1400px or narrower and there are still a good number out there on 1024 wide resolutions.
2. Optimize your images for the web and try and keep them under 100k in file size each so that your site will load quickly. Also, convert your images to 72dpi before uploading. That is the web standard and is what will be displayed no matter what the image is actually set to. All it does on the web is waste bandwidth and slow page loading times.
3. Always save in sRGB, not CMYK or Adobe RGB, or you image colors will turn to muck.
If you are using Photoshop, do a "save for web & devices" from the file menu after sizing your image and it will make sure do the bulk of the work for you (saving in sRGB and at 72dpi).
Last bit: Reboot your internet modem. I have to do that quite often when my connection speeds tank. If you are on a wi-fi hotspot, then you are at the mercy of the equipment there and their connection speed. At Starbucks where I live, when the place is crowded, you might as well forget even sending a single email with just a couple lines of text as it may take 5 minutes.