diff --git a/Controllers/QuoteController.cs b/Controllers/QuoteController.cs
index 17d2e2b..89e4719 100644
--- a/Controllers/QuoteController.cs
+++ b/Controllers/QuoteController.cs
@@ -158,32 +158,47 @@ public class QuotesController : ControllerBase
     /// [AUTHED] Add a new quote
     /// </summary>
     /// <returns>Newly created quote's id</returns>
+    /// <remarks>
+    /// <b>Note</b>: 
+    /// User-provided image URLs are validated by checking
+    /// if they start with "https://", "http://" or "/".
+    /// This is rather a naive solution.
+    /// </remarks>
     /// <param name="request">Form data containing required quote information</param>
     /// <response code="201">Returned on valid request</response>
     /// <response code="400">Returned when any of the categories does not exist</response>
     /// <response code="403">Returned when user's id does not match the creator's id</response>
+    /// <response code="406">Returned when image url is invalid (does not start with "https://", "http://", or "/")</response>
     [HttpPost("new")]
     [Authorize]
     [EnableCors]
     [ProducesResponseType(201)]
     [ProducesResponseType(typeof(ErrorDTO), 400)]
     [ProducesResponseType(typeof(ErrorDTO), 403)]
+    [ProducesResponseType(typeof(ErrorDTO), 406)]
     public async Task<IActionResult> CreateQuote([FromBody] CreateQuoteDTO request)
     {
         // Get user ID from claims
-
         var userIdClaim = User.FindFirst(ClaimTypes.NameIdentifier)?.Value;
         if (userIdClaim == null || !int.TryParse(userIdClaim, out int userId))
             // https://stackoverflow.com/a/47708867
             return StatusCode(403, new ErrorDTO { Status = "error", Error_msg = "Invalid user ID" });
 
-        // Find or create image
+        // Try to find the image inside the DB
         Image? image = null;
         if (!string.IsNullOrEmpty(request.ImageUrl))
         {
             image = await _db.Images.FirstOrDefaultAsync(i => i.Url == request.ImageUrl);
+
+            // Failed? Just insert it yourself
             if (image == null)
             {
+                // Simple (naive) sanity check for image URLs
+                if (   !request.ImageUrl.StartsWith("http://")
+                    && !request.ImageUrl.StartsWith("https://")
+                    && !request.ImageUrl.StartsWith("/"))
+                    return StatusCode(406, new ErrorDTO { Status = "error", Error_msg = "Image URLs should point to http/https url or a local resource" });
+
                 image = new Image { Url = request.ImageUrl };
                 _db.Images.Add(image);
                 await _db.SaveChangesAsync();
@@ -347,13 +362,19 @@ public class QuotesController : ControllerBase
     /// While "categories = null" will not alter the quote's categories,
     /// "categories = []" will (and in turn, empty each and every present category)!<br/>
     /// Be careful when handling user-provided categories!
+    /// <br/><br/>
+    /// <b>Note</b>: 
+    /// User-provided image URLs are validated by checking
+    /// if they start with "https://", "http://" or "/".
+    /// This is rather a naive solution.
     /// </remarks>
     /// <returns>Newly modified quote as a DTO</returns>
     /// <param name="id">Quote to be modified</param>
-    /// <param name="updatedQuote">Updated quote form data</param>
+    /// <param name="updatedQuote">Updated quote form data. Id is ignored.</param>
     /// <response code="204">Returned on valid request</response>
     /// <response code="400">Returned when request text or author is empty (or whitespace)</response>
     /// <response code="404">Returned when no such quote exists</response>
+    /// <response code="406">Returned when image url is invalid (does not start with "https://", "http://", or "/")</response>
     [HttpPatch("{id}")]
     [Authorize]
     [EnableCors]
@@ -385,9 +406,16 @@ public class QuotesController : ControllerBase
         if (!string.IsNullOrEmpty(updatedQuote.ImageUrl))
         {
             image = await _db.Images.FirstOrDefaultAsync(i => i.Url == updatedQuote.ImageUrl);
+
             // Failed? Just insert it yourself
             if (image == null)
             {
+                // Simple (naive) sanity check for image URLs
+                if (   !updatedQuote.ImageUrl.StartsWith("http://")
+                    && !updatedQuote.ImageUrl.StartsWith("https://")
+                    && !updatedQuote.ImageUrl.StartsWith("/"))
+                    return StatusCode(406, new ErrorDTO { Status = "error", Error_msg = "Image URLs should point to http/https url or a local resource" });
+
                 image = new Image { Url = updatedQuote.ImageUrl };
                 _db.Images.Add(image);
                 await _db.SaveChangesAsync();