The best way to do it is to put a Source link and then a link to the copy right license, for example CC0 (these are dead links, but they are just to illustrate the idea :o) ) If you cannot find a copy right license then it is better to not use the image (I am guessing that your first image doesn't have a licence?)

1. We love you more if you link the source and the license :o)
2. So the youtube licenses state that as long as you embed the video in your post that it is then acceptable to use them in the steem-blog context. So no problem there.