Fit, stretch and crop are different operations
Fit keeps the whole image
Fit mode uses a single scale factor for width and height. If the target box has a different shape, one resulting dimension will be smaller than the limit. This is usually the safest option for documents and product photographs.
Stretch changes proportions
Giving an image an unrelated width and height can make circles look oval and letters look compressed. A numerical match is not useful if the subject becomes distorted. Use a proportional method unless distortion is intentional.
Crop fills the box by removing edges
A crop can create a square thumbnail, but it may cut off a label or a design. RSFrameFit avoids that trade-off by retaining the complete frame. If you need exact outer dimensions with padding, use a canvas workflow instead.
Try the workflow
A 3000 × 2000 image fitted inside a 1200 × 1200 box becomes 1200 × 800. The image stays in proportion; the box does not force a square crop.
Open proportional image resizer