I always get the error message when starting the server

05:05 [Error] Failed to call hook 'AddImage' on plugin 'ImageLibrary v2.0.62' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.ImageLibrary.AddImage (System.String url, System.String imageName, System.UInt64 imageId, System.Action callback) [0x00049] in <f41534faf6e64410b687711637406db6>:0
  at Oxide.Plugins.ImageLibrary.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00781] in <f41534faf6e64410b687711637406db6>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <23ba99f131254889867c71f0bd137b1d>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <157a94ee66ab4a7991faecd1eb84be3b>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <157a94ee66ab4a7991faecd1eb84be3b>:0
05:05 [Error] Failed to call hook 'AddImage' on plugin 'ImageLibrary v2.0.62' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.ImageLibrary.AddImage (System.String url, System.String imageName, System.UInt64 imageId, System.Action callback) [0x00049] in <f41534faf6e64410b687711637406db6>:0
  at Oxide.Plugins.ImageLibrary.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00781] in <f41534faf6e64410b687711637406db6>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <23ba99f131254889867c71f0bd137b1d>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <157a94ee66ab4a7991faecd1eb84be3b>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <157a94ee66ab4a7991faecd1eb84be3b>:0

I've got same issue now

I get the same log entries on server startup. 

I believe this is related to missing images that were put onto signs using SignArtist.  They end up being wiped off of the frames/signs after a restart.