Hello,
For the images to look good on the slide background, you need to meet two criteria:
1. Have good image quality, without compression artefacts that may occur after being processed by image compressors.
2. Have an appropriate resolution that covers the entire slide size in height and width on most displays. You can try uploading Slider Images with a minimum size up to 1366×768 pixels
The issue with the image may be due to the inappropriate resolution relative to the slide size. You need to upload images with an appropriate resolution, like the demo, and high resolution and check the issue.
Please read the documentation for more details https://xtemos.com/docs/woodmart/woodmart-slider/
Best Regards,