I guess you are trying policy with WSO2IS. According to policy, It is applicable to "images" resource. You have defined it with target element. But in your request, you are not sending "images"? Therefore policy would not be applicable to this request and there are no other policies in the server that applicable to request, If you want to send a request that would return "permit" according to the your policy, Please try out following request. Here you are sending both "images" and "blue.jpg" a values and modify the attribute id of the subject category.
<Request xmlns="urn:oasis:names:tc:xacml:3.0:core:schema:wd-17" CombinedDecision="false" ReturnPolicyIdList="false">
<Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-category:action">
<Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:action:action-id" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">read</AttributeValue>
</Attribute>
</Attributes>
<Attributes Category="urn:oasis:names:tc:xacml:1.0:subject-category:access-subject">
<Attribute AttributeId="http://wso2.org/claims/role" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">emp</AttributeValue>
</Attribute>
</Attributes>
<Attributes Category="urn:oasis:names:tc:xacml:3.0:attribute-category:resource">
<Attribute AttributeId="urn:oasis:names:tc:xacml:1.0:resource:resource-id" IncludeInResult="false">
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">images</AttributeValue>
<AttributeValue DataType="http://www.w3.org/2001/XMLSchema#string">blue.jpg</AttributeValue>
</Attribute>
</Attributes>
</Request>