Previous and Next links for photoblog

I have some problems concerning navigation in photoblog. On my site I have photos inside post which are gathered inside categories.

1 problem:
My photos inside one category are organized so that first photo in the specific category will be posted “higher” (with older date) so originally wordpress show for next picture link “previous” but actually this is next photo.
How can I change it? Just change the name of the link for “next” but leave the function previous_post()?

2 problem:
I’d like previous/next links will work only inside one category so for the last picture there wouldn’t be “previous” link which will link to first picture inside next category and for the first picture there will not be “next” link also linking to another category.

  1. problem:
    Except for navigation links that appear while displaying picture such as previous_post() and next_post() I would like to have a link to a category of that picture.

Is this possible to make it work without plugins? If so how?
Thanks in advance,