Yes... on this line:
WA_DFP_UploadFiles("WA_UploadResult1", "tip_photo", "0", "", "false", $WA_UploadResult1_Params);
the "0" means overwrite. To rename the new file with a number use:
WA_DFP_UploadFiles("WA_UploadResult1", "tip_photo", "2", "", "false", $WA_UploadResult1_Params);