[_wdh]

The only site I know of that would vaguely fit the bill is https://openclipart.org/. However, it doesn't appear to support searching by image type or by dimension and as far as I can tell, it cannot be 100% guaranteed that you will have all SFW images.

[hysan]

Thanks! This also looks great. Hopefully I won't run into any NSFW images at work.