I am not the copyright/trademark/etc owner of any of these. Use them at your own risk.
If you are the owner and do not want your logo here, please let me know (nicely) and I will be glad to remove it. No lawyers necessary: just submit an issue on github! Just so you know: I am usually using them on a credits page (example), so it might be in your best interests to let me slide. Alternatively, it would be great if you provided the appropriately sized images yourself.
I originally wasn't going to allow hotlinking, but CloudFlare promises unlimited free bandwidth, so I changed my mind. Unless CloudFlare changes their mind, hotlink away!
I am definitely not an artist, and generally do not do anything besides resize and rearrange existing artwork.
It can often be difficult to get the images to looks nice on their own and look good and consistant with the rest of the images.
(and see the next question!)
Vector images look so much better, especially on high-resolution displays, and don't require any of the hacks needed for responsive images: they “just work”!
According to Can I Use, 96% will be able to see them.
Check out the credits page (featuring images from Vector Logo Zone, of course).
Feel free to contact me. Please note that this is just an unpaid sideline, so do not expect an immediate response.