Here's a quick and simple way to do it. Your source image is 640 x 480 and a bit hazy so there is no reason to use a more complex solution.

1. Open your image in GIMP and choose the 'Free Select Tool' F
2. In the tool options choose 'Feather edges', I chose a 10 pixel radius. follow the top, left and bottom edges and the edge of the curb. Once you have selected the area shown below press CTRL + C then CTRL + V to copy and paste it as a new layer.
3. Click the green plus sign in the layers dialog to make the copied portion a new layer. Adjust the levels under Color/Levels (from the top menu) of the pasted layer and the base image until you have what you want.
4. Note the fuzzy edge at the right side of your pasted layer. Once you have both layers' levels where you want them. Right-click on either and select 'Flatten Image'. Then save it. Done.

Here's the one I did as an example. As a side note, if you are able to take the back off of your mobile phone to take the picture you can get significantly clearer images. The hazy effect often comes from the plastic window covering the lens on the battery cover. Remember to hold your battery in place when you take the picture, then put the cover back on. Sounds silly but the improvement is noticeable.