I don't think that illegal characters cause that issue, asdoesn't work, too. I don't know where that object tag comes from, that's why I already suggested to disable the plugin engine and/or undo any modifications.
Sorry, I should have mentioned that I disabled all plugins right away, as you said. There have been no modifications. This is a "pure" 1.4.x install, that has been upgraded to 1.5.x using the guidelines provided by Coppermine.
The weird thing is that it works if you open the images directly (copy-paste the value tag). So it seems to me that only Coppermine is unable to see that those are actual pictures, because of some internal mismatch.
What about all of these:
/include/functions.inc.php
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
Notice line 5795: Undefined index:
Notice line 5795: Undefined index: image
...
I have now enabled debug mode for Everyone, so that you may see the errors for your self.