It doesn't matter whether your blog is here or elsewhere, the issue is copyright law. Any original work is automatically copyrighted the moment the first word is set down.
You have to abide by the copyright and use guidelines on each and every site. There is a section of the copyright laws about fair use, but there is no hard and fast definition about what that is as it depends on the length of the piece and how much you take from it. In general, you are only allowed to quote a small portion in your articles for discussion or review purposes.
I've gone after over 100 that have copied my stuff in its entirety without my permission and in a good number of those cases, the web hosts shut the site down entirely after I filed the DMCA violation notice. Web hosts have to by law or they risk getting their business shut down, or worse having the authorities come after them.