Why getting exception The process cannot access the file image0.gif' because it is being used by another process even if I dispose it first?

Question

private void GenerateAnimatedGifs()
         {
             UnFreezWrapper unfreezWrapper = new UnFreezWrapper();
    
             checkBoxGetImages = false;
             checkBoxGetAllImages.Checked = false;
             GetImagesFiles();
    
             for (int i = 0; i < filesSatellite.Length; i++)
             {
                 Image img = Image.FromFile(filesSatellite[i]);
                 img.Save(filesSatellite[i] + "ConvertedToGif.gif", System.Drawing.Imaging.ImageFormat.Gif);
                 img.Dispose();
    
                 File.Delete(filesSatellite[i]);
             }
    
             GetImagesFiles();
    
             unfreezWrapper.MakeGIF(filesRadar.ToList(), @"d:\Downloaded Images\Animates Gifs\radanim.gif", 100, true);
             unfreezWrapper.MakeGIF(filesSatellite.ToList(), @"d:\Downloaded Images\Animates Gifs\satanim.gif", 100, true);
         }

In the loop I convert each image to gif save it in other name and then dispose the original image and then trying to delete the original image so only the ConvertedToGif images will left.

but I'm getting the exception is being used by another process on the delete line

File.Delete(filesSatellite[i]);

but isn't the file disposed already ?

The problem is that in the constructor I'm loading the images to a pictureBox using timer that is why the images are busy with another process.

If I'm not loading the images at the constructor everything will work fine.

But I want to display the images when running the application and also to be able to convert them to other formats and making other manipulations like creating animated gif of them.

I'm stuck here.

This is the constructor code

public Form1()
        {
            InitializeComponent();

            CheckIfImagesExist();
        }

And the code of the CheckIfImagesExist method

private void CheckIfImagesExist()
        {
            GetImagesFiles();

            if (filesRadar != null)
            {
                if (filesRadar.Length > 1)
                {
                    pictureBox1.Image = new Bitmap(filesRadar[0]);
                    trackBar1.Enabled = true;
                    timer1.Enabled = true;
                }

                if (filesRadar.Length == 1)
                {
                    trackBar1.Enabled = false;
                    pictureBox1.Image = new Bitmap(filesRadar[0]);
                }
            }

            if (filesSatellite != null)
            {
                if (filesSatellite.Length > 1)
                {
                    pictureBox2.Image = new Bitmap(filesSatellite[0]);
                    trackBar1.Enabled = true;
                    timer2.Enabled = true;
                }

                if (filesSatellite.Length == 1)
                {
                    trackBar1.Enabled = false;
                    pictureBox2.Image = new Bitmap(filesSatellite[0]);
                }
            }
        }

The timer tick event

int satImagesCount = 0;
        private void timer2_Tick(object sender, EventArgs e)
        {
            satImagesCount++;

            if (satImagesCount == filesSatellite.Length)
            {
                satImagesCount = 0;
            }

            pictureBox2.Image = new Bitmap(filesSatellite[satImagesCount]);

            if (isInsideSat)
            {
                pb.Image = new Bitmap(filesSatellite[satImagesCount]);

                timer2.Interval = trackBar1.Value * 100;
            }
        }