Example Image Uploader in Visualforce

PageController.apxc

public class PageController {
    // Transient so we don't exceed view state limits
    public transient String fileType { get; set; }
    public transient Blob fileBody { get; set; }

    ApexPages.StandardController controller;
    
    public PageController(ApexPages.StandardController controller) {
        this.controller = controller;
    }
    
    public void saveProductImage() {
        Product2 p = [select id from product2 where id = :controller.getId() for update];
        p.RTA__c = '<img src="data:'+fileType+';base64,'+EncodingUtil.base64Encode(fileBody);
        update p;
        // Get the updated URL so it appears on the page
        p = [select rta__c from product2 where id = :p.id];
        controller.getRecord().put('RTA__c', p.RTA__c);
    }
}

ProductImageUploader.vfp

<apex:page standardController="Product2" extensions="PageController">
    <apex:form>
    	<apex:pageBlock>
        	<apex:pageBlockButtons>
            	<apex:commandButton value="Update" action="{!saveProductImage}" />
            </apex:pageBlockButtons>
          
            <apex:pageBlockSection>
                <apex:inputFile contentType="{!fileType}" value="{!fileBody}" />
            </apex:pageBlockSection>
            <apex:pageBlockSection title="Existing Image" columns="1" collapsible="false">
                <apex:outputField value="{!Product2.RTA__c}" />
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>