I am not entirely sure,I can see there is "photos" which looks like where I should be getting this data from but with virtually no knowledge of php I have no idea how I would go about grabbing photos>photo-url-250 from each offset 01,02,03,04,05 etc.
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"photo-caption":"<p>Here are three different\u00a0coloured\u00a0squares, amazing right<\/p>",
"width":"692","height":"812",
"photo-url-1280":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_1280.png",
"photo-url-500":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_500.png",
"photo-url-400":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_400.png",
"photo-url-250":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_250.png",
"photo-url-100":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_100.png",
"photo-url-75":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_75sq.png","
photos":[
{"offset":"o1","caption":"green square","width":"692","height":"812","
photo-url-1280":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_1280.png",
"photo-url-500":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_500.png",
"photo-url-400":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_400.png",
"photo-url-250":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_250.png",
"photo-url-100":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_100.png",
"photo-url-75":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo1_75sq.png"},
{"offset":"o2","caption":"red square","width":"692","height":"812","photo-url-1280":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo2_1280.png",
"photo-url-500":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo2_500.png",
"photo-url-400":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo2_400.png",
"photo-url-250":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo2_250.png",
"photo-url-100":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo2_100.png",
"photo-url-75":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo2_75sq.png"},
{"offset":"o3","caption":"blue square","width":"692","height":"812","photo-url-1280":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo3_r1_1280.png",
"photo-url-500":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo3_r1_500.png",
"photo-url-400":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo3_r1_400.png",
"photo-url-250":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo3_r1_250.png",
"photo-url-100":"http:\/\/25.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo3_r1_100.png",
"photo-url-75":"http:\/\/24.media.tumblr.com\/tumblr_mdfrfmvBa91rl56bgo3_r1_75sq.png"}]},