It's not good to download a gig image from anywhere.
You can take ideas for gig images from others' profiles, but make sure, never copy the images the same as theirs. Make your gig image unique on your service.
You can make your gig image from canva.com. There are so many templates that will help you to create your gig image. If your know Photoshop, then make your gig image with Photoshop.