I am having the same problem. I am able to add images to articles which show up after CHMOD 777 in media/k2/cache/items.
CHMOD 777 is not desirable though. But even with 777 I am unable to succesfully show category images.
I am able to choose an image. I get no error. Then all I see in backend is the name of the picture, in a boxed frame.

When I enable all options in category (frontend view), all I see is a little box with the name of the picture in it. Not the picture itself.

Any advice would be appreciated.

It seems like I have the same problem.

I use Joomla for about a year, and never seems to have a problem like this on other components that i've been using. Before i've choose to install the K2 component, i was using ZOO application bundled, but they've upgrade the ZOO to work only with mootools 1.2.4 and my template does not suport it, and I dont want to use they're template.

So, when i choose to add a new item in K2, it works normaly, I cand add a title, a text, tag's, etc, but when i go to Image, to upload one image, not a gallery image, i can choose the picture I want, i can add the Item image caption, etc, and when i save this article it apears a blank image.

If i do the same thing to that article, but not add an image, it works perfectly. Any ideas why ?

SOLVED!

At least I can set it up. It is all CMHMOD for me! I was able to add images to articles but not to categories.

In the end I succeeded only after CHMODDING 777 to /media/k2/categories AND /media/k2/items/cache/ AND /media/categories/items/

Because I feel very uncomfertable with 777, I set these back to 755 after uploading all images to categories.
The images still show up.

PLease let me now if this also works for you. I think it will.

It didn't solve the problem if you go in the back-end on components - K2 - information, i get all the necessary diretories as writhable, so it's not that in my case, i just done what you describe, but still not working.

I got the same problem also, the only way I could still publish a image for my items, was to manually create the md5 hash, using an md5 hash generator website (you can find on google) and then duplicate the image file 6 times, and add after the name of each of the files the following suffixes: _Generic, _L, _M, _S, _XL, _XS and upload them to media/k2/items/cache

 

You may also need to upload to media/k2/items/src the image file but without any suffix.

It's a pain but I'm only publishing one item a week or something so I can live with it.

 

The problem only appears to be on the website that is on the public server, on my localhost I can use it with no problems, as long as I resize my pictures to the same aspect ratio as the one appearing on the website.

I tried to chmod, the entire website to 777 and still it's not working so it's not a chmod problem, at lest, not for me.