diff --git a/codex-rs/protocol/src/models.rs b/codex-rs/protocol/src/models.rs
index ff66ed5762..535aa3c9e9 100644
--- a/codex-rs/protocol/src/models.rs
+++ b/codex-rs/protocol/src/models.rs
@@ -4,8 +4,10 @@ use std::io::Read;
 use std::num::NonZeroUsize;
 use std::path::Path;
 
+use codex_utils_image::MAX_PROMPT_IMAGE_FILE_BYTES;
 use codex_utils_image::PromptImageMode;
 use codex_utils_image::load_for_prompt_bytes;
+use codex_utils_image::validate_prompt_image_file_size;
 use serde::Deserialize;
 use serde::Deserializer;
 use serde::Serialize;
@@ -1018,7 +1020,6 @@ const IMAGE_CLOSE_TAG: &str = "</image>";
 const LOCAL_IMAGE_OPEN_TAG_PREFIX: &str = "<image name=";
 const LOCAL_IMAGE_OPEN_TAG_SUFFIX: &str = ">";
 const LOCAL_IMAGE_CLOSE_TAG: &str = IMAGE_CLOSE_TAG;
-const MAX_LOCAL_IMAGE_FILE_BYTES: u64 = 50 * 1024 * 1024;
 
 pub fn image_open_tag_text() -> String {
     IMAGE_OPEN_TAG.to_string()
@@ -1264,30 +1265,15 @@ impl From<Vec<UserInput>> for ResponseInputItem {
                                     "local image path is not a regular file",
                                 ));
                             }
-                            if metadata.len() > MAX_LOCAL_IMAGE_FILE_BYTES {
-                                return Err(io::Error::new(
-                                    io::ErrorKind::InvalidData,
-                                    format!(
-                                        "local image exceeds the {MAX_LOCAL_IMAGE_FILE_BYTES}-byte limit"
-                                    ),
-                                ));
-                            }
+                            validate_prompt_image_file_size(metadata.len())?;
 
                             let capacity = usize::try_from(metadata.len()).unwrap_or_default();
                             let mut file_bytes = Vec::with_capacity(capacity);
                             std::fs::File::open(&path)?
-                                .take(MAX_LOCAL_IMAGE_FILE_BYTES + 1)
+                                .take(MAX_PROMPT_IMAGE_FILE_BYTES + 1)
                                 .read_to_end(&mut file_bytes)?;
-                            if file_bytes.len()
-                                > usize::try_from(MAX_LOCAL_IMAGE_FILE_BYTES).unwrap_or(usize::MAX)
-                            {
-                                return Err(io::Error::new(
-                                    io::ErrorKind::InvalidData,
-                                    format!(
-                                        "local image exceeds the {MAX_LOCAL_IMAGE_FILE_BYTES}-byte limit"
-                                    ),
-                                ));
-                            }
+                            let file_size = u64::try_from(file_bytes.len()).unwrap_or(u64::MAX);
+                            validate_prompt_image_file_size(file_size)?;
                             Ok(file_bytes)
                         });
                         match file_bytes {
@@ -3029,7 +3015,7 @@ mod tests {
     fn local_image_too_large_adds_placeholder() -> Result<()> {
         let dir = tempdir()?;
         let oversized_path = dir.path().join("oversized.png");
-        std::fs::File::create(&oversized_path)?.set_len(MAX_LOCAL_IMAGE_FILE_BYTES + 1)?;
+        std::fs::File::create(&oversized_path)?.set_len(MAX_PROMPT_IMAGE_FILE_BYTES + 1)?;
 
         let item = ResponseInputItem::from(vec![UserInput::LocalImage {
             path: oversized_path.clone(),
@@ -3042,7 +3028,7 @@ mod tests {
                 role: "user".to_string(),
                 content: vec![ContentItem::InputText {
                     text: format!(
-                        "Codex could not read the local image at `{}`: local image exceeds the {MAX_LOCAL_IMAGE_FILE_BYTES}-byte limit",
+                        "Codex could not read the local image at `{}`: image exceeds the {MAX_PROMPT_IMAGE_FILE_BYTES}-byte limit",
                         oversized_path.display()
                     ),
                 }],
diff --git a/codex-rs/utils/image/src/lib.rs b/codex-rs/utils/image/src/lib.rs
index a3f595a183..e28334889a 100644
--- a/codex-rs/utils/image/src/lib.rs
+++ b/codex-rs/utils/image/src/lib.rs
@@ -1,3 +1,4 @@
+use std::io;
 use std::num::NonZeroUsize;
 use std::path::Path;
 use std::sync::LazyLock;
@@ -17,6 +18,8 @@ use image::codecs::webp::WebPEncoder;
 use image::imageops::FilterType;
 /// Maximum width or height used when resizing images before uploading.
 pub const MAX_DIMENSION: u32 = 2048;
+/// Maximum compressed file size accepted for an image added to a prompt.
+pub const MAX_PROMPT_IMAGE_FILE_BYTES: u64 = 50 * 1024 * 1024;
 
 pub mod error;
 
@@ -43,6 +46,17 @@ pub enum PromptImageMode {
     Original,
 }
 
+/// Validates the compressed byte size of an image before prompt processing.
+pub fn validate_prompt_image_file_size(file_size: u64) -> io::Result<()> {
+    if file_size > MAX_PROMPT_IMAGE_FILE_BYTES {
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            format!("image exceeds the {MAX_PROMPT_IMAGE_FILE_BYTES}-byte limit"),
+        ));
+    }
+    Ok(())
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 struct ImageCacheKey {
     digest: [u8; 20],
@@ -57,6 +71,11 @@ pub fn load_for_prompt_bytes(
     file_bytes: Vec<u8>,
     mode: PromptImageMode,
 ) -> Result<EncodedImage, ImageProcessingError> {
+    let file_size = u64::try_from(file_bytes.len()).unwrap_or(u64::MAX);
+    validate_prompt_image_file_size(file_size).map_err(|source| ImageProcessingError::Read {
+        path: path.to_path_buf(),
+        source,
+    })?;
     let path_buf = path.to_path_buf();
 
     let key = ImageCacheKey {
@@ -211,6 +230,21 @@ mod tests {
         encoded.into_inner()
     }
 
+    #[test]
+    fn prompt_image_file_size_limit_is_inclusive() {
+        assert!(validate_prompt_image_file_size(MAX_PROMPT_IMAGE_FILE_BYTES).is_ok());
+
+        let error = validate_prompt_image_file_size(MAX_PROMPT_IMAGE_FILE_BYTES + 1)
+            .expect_err("reject oversized image");
+        assert_eq!(
+            (error.kind(), error.to_string()),
+            (
+                io::ErrorKind::InvalidData,
+                format!("image exceeds the {MAX_PROMPT_IMAGE_FILE_BYTES}-byte limit"),
+            )
+        );
+    }
+
     #[tokio::test(flavor = "multi_thread")]
     async fn returns_original_image_when_within_bounds() {
         for (format, mime) in [