hi,

<apex:page standardController="Lead" extensions="checkbox_Class" showChat="false" showheader="false" sidebar="false" standardStylesheets="false">
       <apex:form id="form1">
         <apex:outputPanel id="Opp1" rendered="{!render1}">
            <apex:commandButton value="Send Pictures" action="{!SendAttachment}"/><br/><br/>
        
                <table width="20%" cellspacing="1px">
                    <tr>
                        <apex:repeat value="{!wrapperList}" var="wrap">
                            <td width="20px">
                            <center><img src="https://c.ap1.content.force.com/servlet/servlet.FileDownload?file={!wrap.wrapAttachfileId}" height="100" width="100"></img><br/>
                            <apex:inputCheckbox value="{!wrap.isSelected }"/></center>
                            </td>
                         </apex:repeat>
                    </tr>
                </table>
            </apex:outputPanel>
         
            <apex:outputPanel id="Opp2" rendered="{!render2}">
                To<label style="color:RED">*</label>:&nbsp;&nbsp;&nbsp;
                <apex:inputText id="emailName" value="{!EmailName}" required="true" size="50"/>&nbsp;&nbsp;&nbsp;
                Email<label style="color:RED">*</label>:&nbsp;&nbsp;&nbsp;
                <apex:inputText id="emailInput" value="{!EmailAddress}" required="true" size="50"/><br/><br/>
             
                <apex:repeat value="{!selectedAttachment}" var="wrap1">
                    <img src="https://c.ap1.content.force.com/servlet/servlet.FileDownload?file={!wrap1}" height="100" width="100"></img>
                 </apex:repeat><br/>
                <apex:commandButton value="Send" action="{!SendEmail}"/>
            </apex:outputPanel>
    </apex:form>
 
</apex:page>

Apex Controller:
public class checkbox_Class
{
    public String propertyId{get;set;}
    public String propertyName{get;set;}
    private final Lead propertyInstance {get;set;}
    @TestVisible public List<wrapper_SendEmails> wrapList {get; set;}
    public List<Id> selectedAttachment {get; set;}
    public String EmailAddress {get;set;}
    public String EmailName {get;set;}
    public Boolean Render1 {get; set;}
    public Boolean Render2 {get; set;}
     
    public checkbox_Class(ApexPages.standardController controller)
    {
          Render1 = true;
          propertyId = (String)controller.getRecord().id;
          propertyInstance = [SELECT id,Name FROM Lead WHERE Id=:propertyId LIMIT 1];
          propertyName = propertyInstance.Name;
    }
 
    public List<wrapper_SendEmails> getwrapperList(){
        System.debug('=='+propertyId);
        if(wrapList == null){
            wrapList = new List<wrapper_SendEmails>();
         
            for(Attachment attachItr : [SELECT id,parentId from Attachment WHERE ParentId=: propertyId ]){
                wrapList.add(new wrapper_SendEmails(attachItr.id));
            }
      }
       return wrapList;
    }
 
    public pageReference SendAttachment(){
        selectedAttachment = new List<Id>();
        System.debug('==='+wrapList);
        for(wrapper_SendEmails attItr : wrapList){
            if(attItr.isSelected == true){
                selectedAttachment.add(attItr.wrapAttachfileId);
            }
        }
        Render1 = false;
        Render2 = true;
        return null;
     }

    public void SendEmail(){
    List<String> EmailStrings = new List<String>();
    EmailStrings = EmailAddress.split(',');
  
 
    try{
       Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
       List<Messaging.Emailfileattachment> fileAttachments = new List<Messaging.Emailfileattachment>();
       for (Attachment attachItr : [SELECT id,Name,Body FROM Attachment WHERE id IN: selectedAttachment])
        {
            Messaging.Emailfileattachment efa = new Messaging.Emailfileattachment();
            efa.setFileName(attachItr.Name);
            efa.setBody(attachItr.Body);
            fileAttachments.add(efa);
        }
        mail.setFileAttachments(fileAttachments);
        System.debug('===email'+EmailAddress);
        mail.setToAddresses(EmailStrings);
        mail.setSubject(propertyName);
        mail.setHtmlBody('Dear '+ EmailName +', <br/>');
        Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
    }catch(Exception e){
        System.debug('====exception'+e);
    }
 
        Render1 = true;
        Render2 = false;
        for(wrapper_SendEmails wraper : wrapList)
        {
        wraper.isSelected = false;
        }
        EmailAddress = '';
        EmailName = '';
        }
  
    @TestVisible public Class wrapper_SendEmails{
        public Boolean isSelected {get;set;}
        public Id wrapAttachfileId {get;set;}
     
        public wrapper_SendEmails(Id attachfileId){
            this.isSelected = false;
            this.wrapAttachfileId = attachfileId;
        }
    }
}


Mytest class

@isTest
public class SendEmail_bb_Test
{
@isTest static void SendEmailTestMethod()
{

     Lead objlead=new Lead(LastName='test      lead',company='vs',Street='test',city='test',postalcode='test',state='ap',country='ind',phone='9948155656');
     insert objlead;
   
     System.currentPagereference().getParameters().put('id',objlead.id);
   
     Attachment objAtt = new Attachment();
     objAtt.Name = 'Test';
     objAtt.body = Blob.valueof('string');
     objAtt.ParentId = objLead.Id;
     insert objAtt;
   
     ApexPages.StandardController sc =new ApexPages.StandardController(objlead); 
     SendEmail_bb b=new SendEmail_bb(sc);
     SendEmail_bb.wrapper_SendEmails sb=new SendEmail_bb.wrapper_SendEmails(objAtt.id,objAtt.Name);
   
     List<SendEmail_bb.wrapper_SendEmails>wrapList=new List<SendEmail_bb.wrapper_SendEmails>();
     wrapList.add(new SendEmail_bb.wrapper_SendEmails(objAtt.id,objAtt.Name));
   
     b.propertyId=objLead.Id;
     b.propertyName=objlead.Name;
     b.EmailAddress='ram@gmail.com';
     b.EmailName='Ram';
     sb.isSelected=true;
     sb.attachName=objAtt.Name;
     sb.wrapAttachfileId=objAtt.id;
   
   
 
 
     b.getwrapperList();
     b.SendAttachment();
     b.SendEmail();
   




}
}