Image Observation: Image Sizes and Alt Tags
One of the most common content optimization techniques is improving the Alt tags of images on Web pages. The Alt tag provides a way to describe images for search engines to better comprehend Web page's content. The Alt tag is also important in regards to accessibility issues.
Today's Web environment of broadband connections and faster servers allows Web designers to spend more freely on Web page's graphic and multimedia content. Few years ago, it was necessary to keep images as small as possible to ensure proper loading of Web pages.
In this post, we look at image size and the use of Alt tags. The samples we use are from small business Web sites and Web 2.0 oriented Web sites. The small business sample is from Web sites having favorable positions with major search engines.
| Table 1: Image Observation - Web 2.0 | ||||||||
|---|---|---|---|---|---|---|---|---|
| Observed Element | Observed Category | % Found | Average | Min | Max | Median | 80 Percentile Range | |
| img | Web 2.0 Oriented | 97.19 | 26.77 | 1.00 | 1,121.00 | 12.00 | 2.00 - 56.20 | |
| Images Count | Web 2.0 Oriented | 92.99 | 12.82 | 1.00 | 84.00 | 1.00 | 2.00 - 33.00 | |
| Images Size | Web 2.0 Oriented | 92.29 | 90,171.18 | 47.00 | 889,321.00 | 6,969.00 | 5,111.00 - 226,272.40 | |
| Images Location | Web 2.0 Oriented | 97.19 | 16,219.39 | 237.00 | 218,145.00 | 5,675.00 | 2,480.80 - 36,022.60 | |
| Alt Count | Web 2.0 Oriented | 19.65 | 15.89 | 1.00 | 232.00 | 2.00 | 1.00 - 44.90 | |
| Alt Length Count | Web 2.0 Oriented | 16.15 | 14.41 | 5.00 | 34.00 | 14.00 | 7.70 - 22.90 | |
| Title Words in Alt | Web 2.0 Oriented | 12.64 | 2.42 | 1.00 | 9.00 | 3.00 | 1.00 - 5.30 | |
| HTML Document Length | Web 2.0 Oriented | 100.00 | 29,261.81 | 1,851.00 | 248,301.00 | 21,121.00 | 5,509.00 - 69,100.80 | |
Table 1 shows that majority of the Web 2.0 Web sites in this sample have 2-56 images, with very high upper ouliers. Approx. 20% use the Alt tag. Images are three times the size of the Html document.
| Table 2: Image Observation - Small Business | ||||||||
|---|---|---|---|---|---|---|---|---|
| Observed Element | Observed Category | % Found | Average | Min | Max | Median | 80 Percentile Range | |
| img | Small Business | 96.71 | 26.78 | 1.00 | 132.00 | 62.00 | 4.00 - 51.40 | |
| Images Count | Small Business | 91.21 | 15.48 | 1.00 | 62.00 | 8.00 | 2.00 - 33.60 | |
| Images Size | Small Business | 87.91 | 87,782.20 | 42.00 | 684,478.00 | 92,846.00 | 4,764.30 - 218,952.40 | |
| Images Location | Small Business | 96.71 | 18,659.00 | 1,062.00 | 110,007.00 | 43,827.00 | 4,376.20 - 40,859.50 | |
| Alt Count | Small Business | 18.68 | 15.41 | 2.00 | 105.00 | 9.00 | 2.80 - 41.00 | |
| Alt Length Count | Small Business | 18.68 | 19.18 | 8.00 | 59.00 | 16.00 | 10.40 - 31.00 | |
| Title Words in Alt | Small Business | 16.49 | 3.80 | 1.00 | 9.00 | 1.00 | 1.00 - 8.40 | |
| HTML Document Length | Small Business | 100.00 | 36,833.53 | 3,789.00 | 220,101.00 | 150,919.00 | 8,192.40 - 73,251.80 | |
Table 2 shows the number and size of images is similar to the Web 2.0 sample. On the other hand small business Web sites with prominent search engine positions are more likely to optimize the Alt tag.
Comparison of various image and Alt tag averages. Both samples are similar with Alt tag length and number of words in Alt tags being the exception.
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