You need to host a picture that is locally stored on your computer to an online site.
I'm usually using that is free (no registration) and reliable.

1- The first step is to host your image stored locally by clicking on "upload images".

2- Click on "browse your computer" that will open a dialog box to navigate through the computer's folders to select the file (your image).

3- Once selected, the window will be refreshed like this. Click on "Start upload".

4- When your image is uploaded, you can crop it to better focus on the subject of the picture. You are going to edit your image. Click on "Edit image".

5- Select the "Crop/Resize" tool. The pointer of your mouse will change to a cross shape. Click on the mouse button and hold it to open a rectangle that will be the new frame of your image.

6- You can adjust each edge of the rectangle for a better fitting. Grab (click and hold) one of a small square.

7- Once reframed as you like, apply the new frame/selection.

8- The size is still a bit too large. It's better when the larger dimension (width or height) is not more 800 pixels. Here I'm changing the larger one (height) to 800 pixels. Mouse -> click in the "height" box -> enter "800" with numeric keypad -> Enter key (or click "Apply").


9- Now you need to "Save" the cropped and resized image. It will save it on IMGUR, not on your computer.

10- Click in the "BBCode (message boards & forums)" frame box to highlight its content.

11- Mouse right click to copy the link, paste it in the window of your message in the Fasttech forum. Done.