Fancy designer box - Jquery Plugin - Large image resizing issue

We purchased Fancy designer box - Jquery Plugin. When try to add a new image to canvas, by clicking ‘Add image’ button, shows an alert message -
‘Sorry! But the uploaded image size does not conform our indication of size.
Minimum Width: 100 pixels
Minimum Height: 100 pixels
Maximum Width: 1500 pixels
Maximum Height: 1500 pixels’

We need to design for images of different resolution.
How can we design with a large size image? Is there any solution? Please reply.