Hello Payam,
You cannot do this since K2 looks for specific filenames.
But in media/k2/items/src you will find the original images, the processed images are in the cache folder.
If you choose to alter the code in the item.php model you will lose all of the image sizes that K2 provides. If size is the question here you can always lower the quality a bit.
JoomlaWorks Support Team
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