When uploading images for use on open house flyers it is best to upload a larger image and not a thumbnail of an image.
So if you are retrieving images from a realtor or builder website and see a bunch of small thumbnail images of the subject property click on the thumbnail to view the larger image. This larger image is the image you want to upload for use on your open house flyer.
The reason for this is that the thumbnail images are too small (don't have enough pixels) and upsize poorly. A larger image has plenty of pixels and will down size much better to fit in the space allowed on the open house flyer.
Here is a video that demonstrates uploading images to an open house flyer: