I have the same problem...
I read in another thread that you can override the edit mode to enable the button. Unfortunatelly there were no answer to that thread.
Ill post if ill find anything...
/Pär
Thanks Pär, and to anyone else with a similar problem, I did raise a support ticket and it was confirmed that the LinkItemCollection does not currently support images. I was going down a route which they also suggested which was to create a custom property inheriting LinkCollection then implementing my own version of PropertyLinkCollectionEditControl.ascx (found in episerver program files). Also need reflector to get anywhere with these. They then suggest passing different parms to the HyperlinkProperties.aspx dialog, image funtionality is toggled in inline js in the dialog but I couldn't work out how to change the params.
Went with, and would recommend, an alternative solution from:
https://www.coderesort.com/p/epicode/browser/EPiCode.ImageListProperty/6.x
NB: Had a bit of fun getting it to work, amended it slightly to include it in my web app project rather than a separate project (as it's meant to work).
Ah ok, I also raised a support ticket, got the same solution you mentioned.
I havent started yet so ill try the image list property intstead as well ;)
Thanks for your reply
/P
I think it says it all in the title... When trying to add a link to link item collection the 'Clickable Image' field is disabled. Am I missing something, or does the LinkItemCollection not support images?