where to ethically source images to then post on pinterest ?

Does anyone know how individuals gather images for Pinterest, particularly for affiliate marketing purposes where repining others' posts redirects traffic to their own blogs? For instance, where can one source images for Pinterest? Is it acceptable to use content from Instagram and repurpose other users' content?Do people simply screenshot and post aesthetic photos as their own from Pinterest , considering it difficult to source specific aesthetic niche images from websites other than Pinterest and Instagram?