Trying to upload my first images and I'm getting this error. They are admittedly large image files. Does Coppermine have a size limit?
Coppermine itself doesn't have specific size limit... But there is a practical limit where your server will exhaust resources (memory,CPU, time out).
Unless you have a need to store/download large versions... It is typically best to resize to a reasonable setting before uploading.
Remember to create thumbnails, GD or Imagemagik needs to load and manipulate the picture...
How large is large?
http://documentation.coppermine-gallery.net/en/upload_troubleshooting.htm#upload_support