Hi marouane,

I have created a sample that you can refer and modify it as per your requirement.

You need to first register and get the clientId using the below link.

https://unsplash.com/join

For documentation refer below link.

https://unsplash.com/documentation#search-photos

For converting the json result returned from the api i have used JSON.Net library.

For more details refer below article.

Read (Parse) JSON data from URL and display in ASP.Net GridView using C# and VB.Net

HTML

<asp:Image ID="imgCity" Height="200px" Width="200px" runat="server" />

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    string clientId = "<Your Client Id>";
    string city = "Mumbai";
    string url = string.Format("https://api.unsplash.com/search/photos/?client_id={0}&page=1&query={1}&per_page=1", clientId, city);
    System.Net.ServicePointManager.Expect100Continue = true;
    System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;
    string json = (new System.Net.WebClient()).DownloadString(url);
    Image image = Newtonsoft.Json.JsonConvert.DeserializeObject<Image>(json);
    imgCity.ImageUrl = image.results[0].urls.small;
}

public class Image
{
    public Result[] results { get; set; }
}

public class Result
{
    public Urls urls { get; set; }
}

public class Urls
{
    public string raw { get; set; }
    public string small { get; set; }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    Dim clientId As String = "<Your Client Id>"
    Dim city As String = "Mumbai"
    Dim url As String = String.Format("https://api.unsplash.com/search/photos/?client_id={0}&page=1&query={1}&per_page=1", clientId, city)
    Net.ServicePointManager.Expect100Continue = True
    Net.ServicePointManager.SecurityProtocol = Net.SecurityProtocolType.Tls12
    Dim json As String = (New Net.WebClient()).DownloadString(url)
    Dim image As Image = Newtonsoft.Json.JsonConvert.DeserializeObject(Of Image)(json)
    imgCity.ImageUrl = image.results(0).urls.small
End Sub

Public Class Image
    Public Property results As Result()
End Class

Public Class Result
    Public Property urls As Urls
End Class

Public Class Urls
    Public Property raw As String
    Public Property small As String
End Class

Screenshot