Proximity implies relation, make sure the elements look related. If not, the meaning could be confusing, appear amateurish or like a mistake. An illustration in a banner won't have the same purpose as a 14px icon in a menu.
It seems the '317Jfez.png' icons are tough to read, due to low contrast and colors might not work well for anyone with colorblindness.
A couple of nice sets are http://glyphicons.com/ (by way of Bootstrap http://getbootstrap.com/components/ ) and http://fontawesome.io/ ...there are a slew of others or you can make your own.
The nice thing about icon fonts is that you can style them using CSS and are resolution independent. This is great because the icons will be consistent with typographic styles, hopefully aiding legibility. Most browsers support webfonts.
I am making alot of assumptions without a better appreciation of how you will use the icons. Hope this was somewhat helpful.