Those images are jpgs images (i.e. bitmapped images) which have probably been exported from a vector graphic design package like Illustrator or Corel Draw, where the design package deals with the images internally as vectors.
If you are searching for such images on sites like stock photo sites, the best term to use is Illustration.
For instance there are similar
building illustrations on istockphoto, provided in vector format so they can be manipulated further in Illustrator or Corel Draw.
So at source, ideally you want the image in vector format, so you can change it, resize it etc, but when it is ready for your website, then you export it to a jpg, png or gif.
It is also possible, and sometimes easier, with more advanced lighting effects, to create these images in a 3D software package, using
3D models with file formats such as 3DS, and then export to jpg, bmp, or perhaps even vector (e.g.
Swift3D).