Stretching happens when width and height are changed independently without preserving the source aspect ratio. A portrait becomes wider, a face looks compressed or a circle turns into an oval. The correct method depends on whether the final box may contain empty space or must be filled completely.
Understand the source aspect ratio
Aspect ratio is the relationship between width and height. A 1200 × 800 image has a 3:2 ratio. Reducing it to 600 × 400 preserves that shape, while forcing it to 600 × 600 changes the ratio and creates a square destination.
When the source and destination ratios differ, one of three things must happen: the image is cropped, empty space is added, or the pixels are distorted. A good resizer makes that choice explicit.
Use contain when the whole image must remain visible
Contain scales the image until it fits completely inside the target dimensions. No content is cropped and the original proportions remain correct. If the ratios differ, empty space appears on two sides.
Contain is useful for product images, logos, diagrams and documents where every edge matters. Choose an appropriate background color or keep transparency when the output format supports it.
Use cover when the box must be completely filled
Cover scales the image until the destination is filled, then crops the excess. It preserves proportions and avoids empty bars, but some content near the edges can be removed.
Cover works well for thumbnails, profile images, cards and hero backgrounds. Position the important subject near the center or crop manually before resizing when faces, products or text must remain visible.
Avoid stretch unless distortion is intentional
Stretch forces the image into the exact width and height even when the ratios differ. It may be acceptable for abstract textures or technical masks, but it is normally wrong for photographs, logos and artwork.
For a strict upload requirement, first crop to the requested ratio and then resize to the exact pixels. This produces a predictable result without changing the shape of people or objects.
- Lock aspect ratio for ordinary resizing.
- Choose contain when nothing may be cropped.
- Choose cover when the destination must be fully filled.
- Crop intentionally before exact square or portrait exports.
- Inspect the downloaded result at the final display size.
Sources and further reading
Technical details were checked against the following primary documentation.
This guide was reviewed for practical clarity and updated for the current NEXDOWNLOAD toolset on July 28, 2026.