You can import images into SketchUp to be used as an image or as texture. Due to graphics driver performance limitations, the maximum size that an image can be in SketchUp is 1024 pixels wide x 1024 pixels high. When you import an image that is larger than that, SketchUp will automatically downsize it using bilinear resampling. But if you want to get the best quality results, it is better to downsize a larger image before importing it into SketchUp. Use a photo editing program like Adobe Photoshop that supports bicubic resampling, and save it as a high quality JPEG file.
In addition, if you are going to use the image as a texture in SketchUp and won't be using the entire image for the texture, it is best to crop the image before importing. This will minimize the impact of the image on your model's file size.
