On Some Entities(Contact,Account,Lead)and custom Entities there is Attribute of "Entity Image"
you can call it using Odata by adding this entity image attribute Schema in you entity
http://<crm address>/XRMServices/2011/OrganizationData.svc/contact?$filter=Name eq test&$select=Name,Entity Image,Content
Or may be possibility is image is save as byte data in Web resource so you have to call web resource to get Image data as
http://<crm address>/XRMServices/2011/OrganizationData.svc/WebResourceSet?$filter=Name eq ‘ts_myPicture.jpg’&$select=Name,Content
Muhammad Sohail