This image is somewhere in the slider:

This is the default image of all our items, which have images, so if you have this image loading on your website, it means, that you have an item on one of your slides, where you haven't selected any image to replace this default one. If you can't see that item, probably it is in a lower z-index position, behind something else, but it's still somewhere on your slide, so you should try to find it in your items list.