I use a cloud-based service called Cloudinary for image storage and manipulation.
1. Go to http://cloudinary.com/ and set up an account.
2. Drag and drop images using the Media Library Side bar:
3. Images can be manipulated using resize and crop; I recommend a width of approximately 600 pixel width for a large-ish landscape image (or height for portrait).
4. Copy and paste the link given into the image display code.
If the image transformation doesn't refresh after resizing, try changing the file format to .png (best for web), or .jpg (good for web).