WordPress define() issue
===

I am having trouble with a php script that I inherited from a previous developer. It is a WordPress site for a real estate company. There is a php script that pulls real estate listings from other other companies that runs automatically twice an hour. There is also a plugin that puts a watermark on pics when photos are uploaded. The watermark needs to be placed on photos that agents upload but not on photos pulled in from the php script.

At the top of the php script he has defines a constant:

    define('MLSP_SKIP_WATERMARK', true);

In the watermarking plugin he checks if the constant is defined:

    if (!defined(MLSP_SKIP_WATERMARK)) {
        do watermarking stuff
    }

It doesn't recognize the constant in the plugin and watermarks all pictures uploaded when the php script is run.

I have tried to move where the constant is defined. It is near the top of the file and not in a function. Is it something with WordPress? I have found similar questions but nothing that has given me an answer. 

Can someone please point me in the right direction?
Thank you.