You can shrink the code down a bit. You can write a function or 2 to essentially do all of this.

Pass the picture box as an object to the function and do your conditionals in that.

I managed to get it down to a few functions. I suggest not using picture boxes with labels on top of them because it just adds to the complexity. I would just change those to buttons.

    using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;



namespace WindowsFormsApplication10

{

    public partial class Form1 : Form

    {

  

        public Form1()

        {

            InitializeComponent();

        }



        private void toggleTabs(object sender,EventArgs e)

        {

            PictureBox pctClicked = (PictureBox)sender;  //Get the object that called this function

            string[] senderPosition = pctClicked.Name.Split('_'; //We want to know what the number is. On the control's name I put an underscore and a number to represent it's position

            tabControl1.SelectedIndex = Int32.Parse(senderPosition[1]) - 1; //The tab control has a selected index property so we can tell it what tab to goto with that

            

        }



        private void mousein(object sender, EventArgs e)

        {

            PictureBox pct_mousedIn = (PictureBox)sender;

            pct_mousedIn.BackColor = Color.Green;

            

        }



        private void mouseOut(object sender, EventArgs e)

        {

            PictureBox pct_mouseOut = (PictureBox)sender;

            pct_mouseOut.BackColor = Color.LimeGreen;



        }

    }







}

Here is the new source:
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There are probably even better ways to do this but I think 20ish lines or whatever it came out to be is alot better than 1200.
This isn't fully functional and you may still need to make changes / finish the code.