diff --git a/flake.nix b/flake.nix
index a7257a5..6acc2d1 100644
--- a/flake.nix
+++ b/flake.nix
@@ -20,7 +20,9 @@
         overlays = [ (import rust-overlay) ];
         pkgs = import nixpkgs { inherit system overlays; };
         stdenv = pkgs.stdenvAdapters.useMoldLinker pkgs.clangStdenv;
-        rustToolchain = pkgs.rust-bin.stable.latest.default;
+        rustToolchain = pkgs.rust-bin.stable.latest.default.override {
+          extensions = [ "rust-src" ];
+        };
 
         nativeBuildInputs = with pkgs; [
           rustToolchain
diff --git a/src/main.rs b/src/main.rs
index 5fc4158..ef26557 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -9,7 +9,7 @@ mod model;
 mod postprocessing;
 mod preprocessing;
 
-use model::{ModelInfo, create_session, get_model_path};
+use model::{ModelInfo, create_session, get_model_path, infer_input_info};
 use postprocessing::{apply_mask, create_side_by_side};
 use preprocessing::preprocess_image;
 
@@ -50,8 +50,8 @@ fn main() -> Result<(), Box<dyn Error>> {
 
     // Load the image
     let img = image::load_from_memory(&bytes)?;
-    let (width, height) = img.dimensions();
-    println!("Loaded image: {}x{}\n", width, height);
+    let (img_width, img_height) = img.dimensions();
+    println!("Loaded image: {}x{}\n", img_width, img_height);
 
     // Get model info
     let model_info = ModelInfo::BIREFNET_LITE;
@@ -63,14 +63,15 @@ fn main() -> Result<(), Box<dyn Error>> {
     // Create ONNX Runtime session
     let mut session = create_session(&model_path)?;
 
-    let input_name = session.inputs()[0].name().to_string();
+    let input_info = infer_input_info(&session, img_width, img_height)?;
 
-    // Preprocess image
-    let input_tensor = preprocess_image(&img, model_info.input_size.0, model_info.input_size.1)?;
+    // Preprocess
+    let input_tensor = preprocess_image(&img, input_info.shape.width, input_info.shape.height)?;
 
     // Run inference
     println!("Running inference...");
-    let outputs = session.run(ort::inputs![input_name => Tensor::from_array(input_tensor)?])?;
+    let outputs =
+        session.run(ort::inputs![input_info.name => Tensor::from_array(input_tensor)?])?;
 
     // Extract mask output
     let mask_output = &outputs[0];
diff --git a/src/model.rs b/src/model.rs
index dc17fff..ec8bad7 100644
--- a/src/model.rs
+++ b/src/model.rs
@@ -1,5 +1,8 @@
 use ort::execution_providers::CUDAExecutionProvider;
-use ort::session::{Session, builder::GraphOptimizationLevel};
+use ort::{
+    session::{Session, builder::GraphOptimizationLevel},
+    value::ValueType,
+};
 use sha2::{Digest, Sha256};
 use std::error::Error;
 use std::fs;
@@ -11,7 +14,6 @@ pub struct ModelInfo {
     pub name: &'static str,
     pub url: &'static str,
     pub sha256: Option<&'static str>,
-    pub input_size: (u32, u32),
 }
 
 impl ModelInfo {
@@ -19,8 +21,7 @@ impl ModelInfo {
     pub const BIREFNET_LITE: ModelInfo = ModelInfo {
         name: "birefnet-general-lite",
         url: "https://github.com/danielgatis/rembg/releases/download/v0.0.0/BiRefNet-general-bb_swin_v1_tiny-epoch_232.onnx",
-        sha256: None, // We'll skip verification for now
-        input_size: (1024, 1024),
+        sha256: Some("5600024376f572a557870a5eb0afb1e5961636bef4e1e22132025467d0f03333"),
     };
 }
 
@@ -157,6 +158,74 @@ pub fn get_model_path(
     Ok(model_path)
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct InputShape {
+    pub batch: u32,
+    pub channels: u32,
+    pub height: u32,
+    pub width: u32,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct InputInfo {
+    pub name: String,
+    pub shape: InputShape,
+}
+
+pub fn infer_input_info(
+    session: &Session,
+    image_width: u32,
+    image_height: u32,
+) -> Result<InputInfo, Box<dyn Error>> {
+    let input = &session.inputs()[0];
+    let input_name = input.name().to_string();
+    let shape = match input.dtype() {
+        ValueType::Tensor { shape, .. } => shape,
+        _ => return Err("Expected tensor input".into()),
+    };
+
+    // Validate shape has 4 dimensions
+    if shape.len() != 4 {
+        return Err(format!("Expected 4D tensor, got {} dimensions", shape.len()).into());
+    }
+
+    // Process each dimension, replacing -1 with appropriate defaults
+    let batch = if shape[0] == -1 {
+        1
+    } else {
+        shape[0].try_into().map_err(|_| "Invalid batch dimension")?
+    };
+    let channels = if shape[1] == -1 {
+        3
+    } else {
+        shape[1]
+            .try_into()
+            .map_err(|_| "Invalid channels dimension")?
+    };
+    let height = if shape[2] == -1 {
+        image_height.min(4096)
+    } else {
+        shape[2]
+            .try_into()
+            .map_err(|_| "Invalid height dimension")?
+    };
+    let width = if shape[3] == -1 {
+        image_width.min(4096)
+    } else {
+        shape[3].try_into().map_err(|_| "Invalid width dimension")?
+    };
+
+    Ok(InputInfo {
+        name: input_name,
+        shape: InputShape {
+            batch,
+            channels,
+            height,
+            width,
+        },
+    })
+}
+
 /// Create an ONNX Runtime session from model path with CUDA backend
 pub fn create_session(model_path: &Path) -> Result<Session, Box<dyn Error>> {
     println!("Loading model into ONNX Runtime with CUDA backend...");