Image source and alt attribute in HTML - Browser Rendering Trace

Render Flow - Image source and alt attribute

[Read <img>] -> [Parse src attribute] -> [Request image from URL] -> [Load image data] -> [Render image box] -> [Display alt text if image fails]

The browser reads the <img> tag, fetches the image from the src URL, and displays it. If the image can't load, the alt text is shown instead.

Render Steps - 3 Steps

Code Added:<img src="https://example.com/cat.jpg">

Before

[Empty page]

→

After

[Image box with cat picture]

The browser loads and shows the image from the src URL.

🔧 Browser Action:Fetches image data and paints image on screen

Code Sample

This code shows a cat image. If the image can't load, the text 'A cute cat sitting on a sofa' appears instead.

HTML

<img src="https://example.com/cat.jpg" alt="A cute cat sitting on a sofa">

Render Quiz - 3 Questions

After step 1, what do you see on the page?

A The alt text displayed

B The cat image displayed

C An empty box with no content

D A broken image icon

Common Confusions - 2 Topics

Why do I see a broken image icon instead of the alt text?

Some browsers show a broken image icon plus the alt text or only the icon. The alt text is always available to screen readers even if not visible.

💡 Alt text is for accessibility and fallback, but visible fallback depends on browser.

Does the alt text show when the image loads correctly?

No, the alt text is hidden when the image loads successfully. It only appears if the image cannot be displayed.

💡 Alt text is invisible if image loads, visible only on failure.

Property Reference

Attribute	Purpose	Visual Effect	Accessibility Benefit
src	URL of the image to display	Shows the image from the URL	N/A
alt	Text description if image can't load or for screen readers	Shows text if image fails	Describes image for screen readers

Concept Snapshot

The <img> tag uses src to show an image from a URL. The alt attribute provides text if the image can't load. Alt text is also read by screen readers for accessibility. If the image loads, alt text is hidden. If the image fails, alt text is shown instead.

Practice

1. What does the alt attribute in an <img> tag do?

easy

A. Provides a text description of the image for screen readers and when the image can't load

B. Specifies the URL of the image to display

C. Sets the size of the image on the page

D. Adds a border around the image

Solution

1. Step 1: Understand the purpose of the alt attribute

   The alt attribute provides alternative text describing the image content.

2. Step 2: Recognize its use for accessibility and fallback

   This text helps screen readers and shows if the image fails to load.

3. Final Answer:

   Provides a text description of the image for screen readers and when the image can't load -> Option A

4. Quick Check:

   alt describes image content [OK]

Hint: Alt text describes images for accessibility and fallback [OK]

Common Mistakes:

• Confusing alt with src attribute
• Thinking alt controls image size
• Using alt to add styling

2. Which of the following is the correct syntax to add an image with source "photo.jpg" and alt text "A sunset"?

easy

A.

B.

C.

D.

Solution

1. Step 1: Identify correct tag and attributes

   The correct tag is <img> with attributes src and alt.

2. Step 2: Check attribute names and order

   <img src="photo.jpg" alt="A sunset"> uses correct attribute names and syntax: src="photo.jpg" and alt="A sunset".

3. Final Answer:

   <img src="photo.jpg" alt="A sunset"> -> Option A

4. Quick Check:

   Correct tag and attributes = <img src="photo.jpg" alt="A sunset"> [OK]

Hint: Use <img> with src and alt attributes exactly named [OK]

Common Mistakes:

• Using <image> instead of <img>
• Using 'source' instead of 'src'
• Using 'description' instead of 'alt'

3. What will the browser display if this code is used and the image file "logo.png" is missing?

<img src="logo.png" alt="Company Logo">

medium

A. Nothing will show, just empty space

B. The browser will crash

C. An error message will pop up

D. The text "Company Logo" will appear instead of the image

Solution

1. Step 1: Understand what happens when image source is missing

   If the image file can't be found, the browser shows the alt text as a fallback.

2. Step 2: Identify the alt text in the code

   The alt text is "Company Logo", so this text will display in place of the missing image.

3. Final Answer:

   The text "Company Logo" will appear instead of the image -> Option D

4. Quick Check:

   Missing image shows alt text [OK]

Hint: Missing images show alt text in browser [OK]

Common Mistakes:

• Expecting no output or blank space
• Thinking browser shows error popups
• Assuming browser crashes

4. Find the error in this image tag:

<img src="picture.jpg" alt>

medium

A. The img tag should be closed with

B. The src attribute is misspelled

C. The alt attribute is missing a value

D. The alt attribute should be written as alt-text

Solution

1. Step 1: Check the alt attribute syntax

   The alt attribute is present but has no value assigned, which is invalid.

2. Step 2: Confirm correct attribute names and tag usage

   The src attribute is correct, and <img> is self-closing, so no closing tag needed.

3. Final Answer:

   The alt attribute is missing a value -> Option C

4. Quick Check:

   Alt attribute must have a value [OK]

Hint: Alt attribute always needs a descriptive value [OK]

Common Mistakes:

• Leaving alt attribute empty
• Adding closing tag
• Changing alt attribute name incorrectly

5. You want to add an image that shows a cat playing with a ball. Which is the best way to write the <img> tag for accessibility and SEO?

hard

A.

B.

C.

D.

Solution

1. Step 1: Understand the purpose of alt text for accessibility and SEO

   Alt text should clearly describe the image content to help screen readers and improve search engine understanding.

2. Step 2: Evaluate the options for descriptive quality

   <img src="cat-ball.jpg" alt="Cat playing with a ball"> describes the image specifically as "Cat playing with a ball", which is clear and meaningful.

3. Final Answer:

   <img src="cat-ball.jpg" alt="Cat playing with a ball"> -> Option B

4. Quick Check:

   Descriptive alt text improves accessibility and SEO [OK]

Hint: Use clear, specific alt text describing the image content [OK]

Common Mistakes:

• Using vague alt text like 'image' or 'cute'
• Omitting alt attribute entirely
• Using unrelated or too short alt text