This seems to be a very odd intermittent problem only for users on mac.
We have found a couple of things that have resolved it for other customers.
Please try the following options below
Make sure you click "Open" when inserting a picture rather than double clicking on it. DO NOT use "copy & paste" to insert images, this will cause a problem.
Make sure that you have saved Craft Maker Pro to a location other than the downloads folder. Please check the read write folder permissions of the folder that Craft Maker Pro is installed in and ensure that they are set to read and write.
Please see here for instructions on how to check this - How to set Read and Write Pemissions.
If that doesn't fix it I have had a customer who had this problem before and after some consultation with Apple found the way to resolve it was by changing the system user.
In Craft Maker Pro go to "File" and "Preferences" then under the General Tab change the user to "Other".
If neither of the above work, log out of the computer and log back in. Go to PARTS and add a picture. Then go to PIECES and add a picture and then everything should work as normal again.
If these still don't work then please delete your original installation of Craft Maker Pro and re-install again from scratch. If you already have data in there that you wish to keep please check our support section on how to backup your data BEFORE you delete you current installation.