These are two, quick and simple sites for posting an image online (temporarily). It doesn't get much more simple than this. The front page of each site has an upload field, and after you upload the image it gives you the image's URL. No signing up or other hassle involved.
Both sites are for temporary image upload, so it's not particularly useful for blogs, but it is good if you're trying to:
a) post an image to a message board, auction, invite service, etc...
b) exchange an image with a group of people
Of the two, tinypic seems better, if only because the describe they terms of their service -- images removed after 30 days of no hits or after 10,000 hits -- and their UI is ever-so-slightly more polished. It's not clear what TechImage's rules are. Tinypic also allows you to upload via URL, and the image URLs it generates are, well, tiny (e.g. http://tinypic.com/99b5).
I hope services like these become more prominent; a fair amount of bandwidth on my site is taken up by people posting images from my Web site directly to message boards.