Hi davesieg, klaver and emimi (and Gary, of course ):
This issue might very well be related to the problem with encondings in the database introduced in Tiki5.0 under certain specific scenarios (yours might be one of them). As fas we now, most (if not all) problems with encodings are solved in Tiki 5.1, after the hardwork of some developers in TikiFestBarcelona2 some weeks ago.
Tiki 5.1 should be released very soon.
If you could test upgrading a copy of your site & db to Tiki 5.1 and see if it also fixes your problems with image uploads, it would be awesome.
You can download at any time a pre-release tarball from:
which will lead you to:
Hope this helps, and please report back with the results of your test.