What is the difference between an image compressor and an image resizer?

An image compressor reduces file size (in KB or MB) by removing redundant visual data while keeping pixel dimensions unchanged. An image resizer changes the actual pixel dimensions (width × height) of an image. For example, compressing a 4000×3000 pixel photo might keep the same dimensions but reduce the file from 8MB to 2MB. Resizing would change it to 1200×900 pixels, reducing dimensions regardless of file size. Both tools complement each other: resize first to appropriate dimensions for your use case, then compress for the smallest possible file size.