Summary
Email spam filters actively scan image content and QR codes using various methods, including OCR to detect suspicious text and patterns. While sophisticated, effective image scanning is resource-intensive, and the level of analysis can vary based on factors like DMARC passing status. Filters look for suspicious content, malicious code, policy violations, high image-to-text ratios, and problematic QR codes. Optimizing images, using descriptive alt text, balancing text and images, using QR codes carefully, and avoiding malicious content are essential for deliverability. Spammers historically used images to bypass filters, but modern OCR technology counteracts this, flagging such attempts.
Key findings
- Image Scanning is Common: Various email platforms like Gmail and Exchange Online actively scan images.
- OCR is Used: Optical Character Recognition (OCR) is used to analyze images for text.
- QR Codes are Suspect: QR codes can be red flags, particularly if linking to unfamiliar or suspicious domains.
- Alt Text is Important: Descriptive alt text is crucial; missing or irrelevant alt text can trigger spam filters.
- Image Size Matters: Large image sizes can negatively impact deliverability.
- DMARC Impact: Emails that are DMARC compliant are less likely to be scrutinised.
Key considerations
- Optimize Images: Optimize images for size and resolution to avoid triggering spam filters.
- Use Alt Text: Use descriptive and relevant alt text for all images.
- Balance Text and Images: Maintain a balance of text and images to avoid being flagged as spam.
- Use QR Codes Carefully: Use QR codes sparingly, ensuring they link to reputable sites.
- Avoid Malicious Content: Ensure images don't contain malicious code or violate email service provider policies.
- Watch Image-to-Text Ratio: Be mindful of the image-to-text ratio, as high ratios can raise suspicion.
What email marketers say
9 marketer opinions
Email spam filters actively scan image content and QR codes, employing techniques like OCR to detect suspicious text and patterns within images. While images were once used to bypass text-based filters, modern filters now scrutinize them closely. QR codes, especially those linking to unfamiliar domains, can also raise red flags. Factors such as image size, the presence and relevance of alt text, and the overall balance of text and images in an email impact deliverability.
Key opinions
- Image Scanning: Spam filters scan images for suspicious content and patterns.
- QR Code Scrutiny: QR codes in emails can be a red flag, particularly if linking to unfamiliar domains.
- OCR Technology: OCR (Optical Character Recognition) is used to analyze text embedded within images.
- Alt Text Importance: Descriptive alt text is crucial; missing or irrelevant alt text can trigger spam filters.
- Image Size Impact: Large image sizes can negatively impact deliverability.
Key considerations
- Optimize Images: Optimize images for size and resolution to avoid triggering spam filters.
- Use Alt Text: Use descriptive and relevant alt text for all images.
- Balance Text and Images: Maintain a balance of text and images to avoid being flagged as spam.
- QR Code Caution: Use QR codes sparingly, ensuring they link to reputable sites.
- Reputable Links: Ensure all links, including those within QR codes, lead to reputable domains.
Marketer view
Email marketer from Email Geeks shares that Proofpoint does QR analysis.
13 Jul 2023 - Email Geeks
Marketer view
Email marketer from EmailOctopus explains that using descriptive alt text for images is crucial. Spam filters often look for missing or irrelevant alt text as a sign of spam.
1 Nov 2023 - EmailOctopus
What the experts say
5 expert opinions
Email spam filters do scan images, using various methods, including OCR to detect text. However, in cases of DMARC passing emails from known entities with high mail volume, in-depth content analysis is less likely. While effective image scanning is computationally expensive, filters look for suspicious text, high image-to-text ratios, and the presence of QR codes, which can be considered suspicious. Spammers have used image-based spam to evade filters, but modern filters use OCR to counteract this.
Key opinions
- Image Scanning Occurs: Email spam filters scan images using various methods.
- OCR Usage: OCR (Optical Character Recognition) is used to detect text within images.
- DMARC Impact: DMARC passing emails from known entities might receive less in-depth content analysis.
- Scanning Cost: Effective image scanning can be computationally expensive.
- QR Code Suspicion: The presence of QR codes can be considered suspicious.
Key considerations
- Monitor Image-to-Text Ratio: Be aware that filters might flag messages with high image-to-text ratios.
- Use QR Codes Carefully: Use QR codes cautiously, as their presence can raise suspicion.
- Understand DMARC Implications: Consider that DMARC passing status may influence the level of content analysis performed.
- Be Aware of OCR: Understand that OCR is used to detect text within images, so avoid embedding spammy text.
Expert view
Expert from Spam Resource explains that spammers have employed image-based spam, embedding text within images to evade traditional text-based filters; however, modern spam filters utilize OCR to analyze these images.
25 Aug 2024 - Spam Resource
Expert view
Expert from Email Geeks explains that scanning images in any useful way is fairly expensive.
10 Nov 2022 - Email Geeks
What the documentation says
4 technical articles
Various email platforms like Gmail and Exchange Online actively scan images for suspicious content, malicious code, and policy violations, aiding in spam and malware detection. Advanced spam filters, as highlighted by Spamhaus, utilize OCR (Optical Character Recognition) to analyze images for embedded text, identifying potential spam indicators. Apache's Spamassassin can also be configured to perform image checks using OCR, extending the capability to scan images for content.
Key findings
- Gmail Image Analysis: Gmail's spam filters analyze images for suspicious content, including embedded text and unusual patterns.
- Microsoft Exchange Protection: Exchange Online Protection scans images for malicious code and content that violates their policies.
- Spamhaus OCR: Advanced spam filters use Optical Character Recognition (OCR) to analyze images for text content.
- Spamassassin Configuration: Spamassassin can be configured to check images using OCR.
Key considerations
- Image Content: Ensure images don't contain suspicious or misleading content.
- Avoid Malicious Code: Verify images are free from malicious code to prevent malware filtering.
- Review Policy Compliance: Confirm images comply with the policies of email service providers.
- Configure Spamassassin: Consider configuring Spamassassin with OCR for enhanced image analysis.
Technical article
Documentation from Apache explains that it is possible to configure Spamassassin to check images using OCR.
30 Aug 2022 - Apache
Technical article
Documentation from Spamhaus indicates that advanced spam filters use optical character recognition (OCR) to analyze images for text content and identify potential spam indicators.
6 Feb 2024 - Spamhaus
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